Looking at it from the otherside, what incentive is there for them to pay teams developers to build Unreal Engine, and then let you use the technology for free and get nothing when your product takes off?

By all means, if you don't like the terms don't use the engine, but it's hard to take it seriously when you make it sound as if you're doing them a favor using their engine for free.

Oh I understand it's a business. I'm just making it clear why I'm not biting, on the off chance Epic employees are here.

Businesses should study their markets. Sadly, many people in the market are completely fine giving away things to get shiny, even giving up revenue. So until standards of customer treatment rise, we'll be dealing with various levels of SaaS.

Except some of us just aren't buying anything, due to the terms and lacking perceived value.

If Unreal works for you that's fine. Why do I have to like or buy it?

Unreal can make your game possible in the first place depending on your required functionality, timeline, and budget. That can be a mightily powerful incentive.

What does Unreal provide that other engines can't?

An unreal amount more. No - seriously. It practically has everything you need to build a game. I guess a clear and easy way to learn it though.. that it cannot seem to provide.