Some of those games were certainly not low effort, though. The Jedi Knight games for example. I spent a few months of my spare time modding Jedi Knight Academy

Some of those games were certainly not low effort, though. The Jedi Knight games for example. I spent a few months of my spare time modding Jedi Knight Academy and from familiarizing myself with the code base I can tell you they put a lot of effort into it. And while it's based on id Tech 3 it very much has its own feel.