Author of Pydantic here, very sorry you've had problems migrating. We were very aware this was going to cause problems, and have done our best to make migrating easier. I truly believe that v2 will be a big improvement.

I think there are two things going on:

1. Python: Python's laxness doesn't make it easy to define strict APIs or know when you're breaking them. The lack of export controls also means defining what's in the API and what's not is hard. Also Python's strong introspection makes it possible to do crazy things further blurring the API boundary.

2. The ecosystem: with pydantic as an example - the library has grown enormously, more than I ever imagined from an experiment in a file in another project to a major library used by thousands of millions of developers, for a very wise range of applications. I never imagined that happening, do I didn't think all that hard about the interface at the beginning, or even at the v1 release. I also knew much less back then.

I'm not sure this kind of growth is very common in other languages except JavaScript.

(Written on my phone, sorry for typos)