You never worked onrold code. It’s never that simple in practice when you have to make changes to existing code without breaking or rewriting everything.

Sometimes the client wants a new feature that cannot easily implement and has to do a lot of different DB lookups that you can not do in a single query. Sometimes your controller loops over 10000 DB records, and you call a function 3 levels down that suddenly must spawn a new DB query each time it’s called, but you cannot change the parent DB query.