For quite a long time, the private ownership of a car had been praised as a status symbol. Mechanical complexity and the inherently high maintenance cost had made it harder for lower-income Europeans to afford it, plus there was another risk of engine damage due to freezing of the cooling water when parked outside in the winter. In times when antifreezing radiator fluids were seen as quite of a sci-fi deal, the release of economy cars with air-cooled engines such as the Volkswagen Beetle and the motorcycle-engined BMW Isetta meant that it would finally become technically viable for many who couldn't afford havign a heated garage at home.
Even though the Isetta was not so conventional at all, being available either in the 4-wheel version with a narrower rear track in order to not require an open differential or in a 3-wheel version catering to markets where the register as a motorcycle led to a lower licensing cost, not just the perceived status of a car but also concerns about stability turned the 4-wheel into a more desirable option. The enhanced comfort in rain and snow was clearly an advantage compared to a motorcycle with sidecar, which until the postwar used to be the main alternative for those who needed an improvement to either the cargo or passenger capacity and couldn't afford to own a conventional car, but it's possible that showing off aboard something peceived as "superior" to a motorcycle could be an even stronger sales argument...
The same perception that led 4-wheel vehicles to be regarded as more desirable echoed to a much lower extent to commercial operators in a worldwide basis, to a point that certain tricycles such as the Piaggio Ape and its Indian derivatives even became praised as some sort of cultural icon. Advantages such as a lower fuel consumption and a fewer amount of components that would need replacements such as tyres, springs, shocks and brake pads are a valuable asset to enhance the profitability, and nowadays those seem to be more likely to increase the presence of 3-wheel vehicles as a cost-effective response to stricter environmental standards affecting the cars and light commercial vehicles market. Passenger applications are still a taboo in some countries, not just developed ones such as Australia and the United States but even third-world ones like my homeland Brazil where the Indian "tuk-tuk" grabbed more attention after being featured in an India-themed soap-opera but is still faced more as a curiosity than as an effective option to enhance urban mobility.
Naturally, the low performance of a "tuk-tuk" is a downside while looking for a vehicle suitable not just to city traffic but also to occasional road trips, with this kind of compromise being undesirable for customers who wouldn't afford to own a second vehicle dedicated to go through longer distances at higher speeds. On the other hand, pointing out the 3-wheel layout as unsuitable to road traffic without a compromise to the safety is not accurate at all, as it have been already proven by so many Volkswagen-based custom trikes. Inherent risks of the all-open seating area usually featured on them shall not be disconsidered, but are far from being reasonable grounds to rule 3-wheel vehicles out.
The popularity of small coupé-utilities, which raised from a low-cost alternative aimed at commercial operators to a somewhat trendy option for those who want to pose as a "gas-station cowboy", can be seen as a precedent to an eventual increase to the acceptance of utility tricycles among private users. It's already happening in Uruguay, where the lower purchase price and running cost of Chinese-made cargo tricycles with a fully-enclosed cabin featuring car-like controls have turned them into a viable option to replace badly worn-out older vehicles with comparable capabilities. The improvements to the fuel-efficiency are also noticeable, with a decrease in emissions as a secondary advantage. Sure there are some political and cultural factors that lead this option to a wider acceptance in Uruguay, ranging from the lack of a protectionist policy aimed at the nearly-defunct local auto industry to the higher degree of success in the "whitening" policies enforced in most South American countries right after the abolishment of slavery to a point that it's not so usual to spot a black Uruguayan (even a kid who tried to sell me weed a few years ago was white), but it doesn't seem impossible to eventually become more accepted in Brazil too. For those who either can't afford a 4-wheel vehicle or just look for some inexpensive commuter, it's not a bad choice at all.
Sidecars and some crude tricycle conversions became more widespread in Brazil in the last 10 years, mostly based on low-displacement motorcycles and catering to commercial operators but, due to the skyrocketing fuel costs and the scarcity of parking spots on the streets, the lower fuel consumption and smaller footprint have turned these alternatives more attractive to private users too. Once again the lack of weather protection is somewhat undesirable, but it still doesn't outweight the savings. While it's still more usual to see it used to deliver bottled water and propane, the popular perception of this device as a makeshift is quickly fading away. The outrageous prices of a brand-new car is also leading sidecars to become an alternative for novice motorcycle users looking for a small boost to the passenger capacity at a total cost that remains proportionately lower.
Unfortunately, the average mentality in Brazil goes beyond the perception of the car ownership as a matter of status, even though it's just a local penalty-box such as the Chevrolet Celta or an old import worn-out to the point that it would be more valuable if parted-out. The main reason for many people in Brazil to get a car is to show-off to neighbors or to the "gas whores", and there is always some lame excuses given when somebody's bad taste for cars is addressed. It's not unusual for Brazilian ricers to act like spoiled children and label every criticism as "envy", even if the money blown in their failed attempts to improve the looks of their rides could be better spent upgrading to a stock one of a higher segment instead, but it just serves to point that reasonability is not always treated as a priority by those looking to get a car.
Anyway, despite some calls for a performance improvement desirable to keep up with road traffic, and therefore increase their overall versatility, tricycles and sidecars have already proven their value as an asset to raise the efficiency of the urban mobility. So, in many circumstances, it's not a higher amount of wheels what could define which vehicle is "better".
