the business model is.
provide awesome features. get paid from game companies to make them work properly and have perfect performance.
if you need that extra 20% to get to 100% then you need to pay.
from my understanding on how this entire game engine industry works is to think at it like this:
They give you all the ingredients to make a perfect 5 star meal, but they hide the recipe.
Almost every piece of the engine has some ideal setup where it works perfectly as it should. Multiply this with tweaks you need to made to have more engine parts work together, again with an ideal unknown settings setup.
Things quickly get out of hand when you don’t know what you are doing, like me, and you learn game design learning from youtube videos.