The Stackoverflow schema is decent. Especially for someone that is a relative amateur to study. It's nothing special or complex, however it's a good example of something that actually works well in practice (and at massive scale). The CRUD-CMS Q&A style lends itself nicely to a basic db schema that is easy to get your head around at a glance.
Seeing some training sessions on performance tuning that use this database as the example, an educated guess is that it's done on purpose. I saw a few cases where usual rules have to be bent to get functionality, sometimes reality beats the book.
https://meta.stackexchange.com/questions/2677/database-schem...
https://i.stack.imgur.com/AyIkW.png
19 million questions, 29m answers, 12m users, 10m visits per day, and most of the db action is in less than two dozen tables.