> It turns out that it makes it really hard to share people, libraries, and learning between teams
The idea is that you don't do that. It's a matter of duplicating functionality across teams so that each team isn't beholden to another team. pushing that library doesn't suddenly break things, for example.
Whether you agree with it or not, when you choose microservices, you choose to avoid sharing libraries like that. In the small it's probably ok (across microservices in 1 team, depending on circumstances), but in the large the gain isn't worth the added maintenance hassle.