Why would I not be so tempted to replace the engine of an Opel Corsa B for a more modern one?

A car which became somewhat like a Volkswagen Beetle replacement in countries such as Mexico, and to a smaller extent my homeland Brazil, rebadged as a Chevrolet, the Opel Corsa B has a pretty reliable and no-nonsense engine, which may be more friendly to a shade-tree mechanic than it appeared when it introduced electronic fuel injection to entry-level cars in Brazil. In contrast to Mexico where both 1.4L and 1.6L variants were more common by a fair margin, both engines with either throttle-body injection or multi-port according to different model-years, the 1.4L was overshadowed in Brazil not only by the 1.6L bur also by the Brazil-specific 1.0L which was also a 4-cylinder, in contrast to some post-facelift European versions which resorted to a 3-cylinder 1.0L engine. Even though all the engines fitted to the Brazilian and Mexican Chevrolet-rebadged versions of the Opel Corsa B were more orthodox than the Volkswagen Beetle's engine, which would make other conservatively-designed engines sound easier to assimilate once swapped into a Corsa, maybe it wouldn't be great to replace it with a more modern one.

The timing belt not being of the oil-bath type, which is a plague of so many modern small engines, may be a reason to single out a replacement engine from GM itself for instance, as the easier to fit inside the engine bay of the Opel Corsa B would be the 3-cylinder 1.0L and 1.2L used in models such as the Onix and the Tracker. Had those engines been fitted with a timing chain instead, just like the Fiat GSE engine which is available as either 3-cylinder 1.0L or 4-cylinder 1.3L both naturally-aspirated or turbocharged, maybe it would be easier to assimilate such engine swap, because the wet-belt design being much more sensitive to the specifications of the engine oil makes it less "Brazilian-proof" than it should be. Other options such as engines from Japanese manufacturers with a timing chain instead of a timing belt, into a car which still seems to have been the last effective chance GM had to remain competitive against its Japanese and Korean contenders on entry-level cars, it would be quite strange to fit an engine from the "enemy" into an Opel Corsa B...