Unfortunately, UUID as PK is an extremely common pattern these days, because devs love to believe that they’ll need a distributed DB, and also that you can’t possibly use integers with such a setup. The former is rarely true, the latter is blatantly false.
The takeaway here is that they weren't mature enough to realize they were, in fact, doing something "weird". I.e. Using UUIDs for PKs, because hey "Netflix does it so we have to too! Oh and we need an engineering blog to advertise it".
Edit. More clarity about why the UUID is my point of blame: If they had used a surrogate and sequential Integer PK for their tables, they would never have to tell SQLAlchemy what the default would be, it's implied because it's the standard and non-weird behavior that doesn't include a footgun.