Bikini Jetpack (Flappy Bird-like game)

The underlying code is as much part of the product as is the art and sound. If you aren't given the freedom of at least having the option of looking at and/or modifying the built-in functions, then you don't really have complete creative control.

So would you rather there be no option for aspiring developers with no large sums of cash to throw at a product they know nothing about? Because that's the deal with every other powerful engine.

The others might have a small trial, but in the end you have to pay upfront or get nothing, and then usually after that the developers of the engine continue to take from any sales you may or may not get. Unity may not be perfect but it's by far the best choice for a team/person with barely any starting funds, whether you like it or not.