They end up doing a lot of things that are only applicable to their situation, and couldn’t be used to make a much more powerful operating system. For example, they might look for ways to recycle pieces of code, and make particular pieces of code do as many different things in the program as possible.

It seems to me that finding out how to recycle code and making particular pieces of code do many different things is exactly how to build a more powerful (and general) operating system.