What saddens me the most is to see those kids who grew up with a smartphone in their hand trying to convert a picture by renaming it. It is a problematic form of computer illiteracy.
There are lots of website and apps where renaming the file is the best solution for an enduser, because of systems that are the counter part of this that limit the option on the frontend but allow it on the backend.
There’s no reason why any system should care about a file’s extension type. It’s meaningless.