Normally, people don't do this a) because they don't want to be required to deal with the cruft or b) because they believe someone will observe their bad behavior and stop it. They don't really have to deal with the cruft, and it's clear now that no one in this organization will hold them accountable, so why should they waste time and energy trying to build a consistent platform?

re: Conway's Law, the organization's communication mechanisms are loose and ad-hoc; there is no central coordination. Consequently, the software is coordinated on a loose, ad-hoc basis between small teams. The same featureset will be implemented 4 times by 4 different teams, not because they can't talk (there is an office where most people hang out together all day, and people do generally keep an awareness of what the other group is working on), but because they'd rather just do it the way they want to do it.

It's not that no one ever ends up sharing anything. It's just that instead of having a discussion and making consistent decisions about the platform, they just do what they want, because they can.