> How on earth is this not practical?

Fine, but you still need to read in those 100+ fields. So now you gotta contend with 20+ joins just to pull in one record. Not more practical than a single SELECT in my opinion.

You don't need to join what you don't actually need. You also need to be careful writing your queries, not just the schema. The most common ones should be wrapped in views or functions to avoid the problem of everyone rolling their own later.

Performance generally isn't an issue for an arbitrary number of joins as long as your indices are set up correctly.

If you really do need a bulk read like that I think you want json columns, or to just go all in with a nosql database. Even then, the above regarding indexing is still true.