Earlier quoted context omitted.
I definitely support making your own game engine if you enjoy it as a programmer. But it shouldn't be a surprise that it's not the best choice for the most developers. Every moment you're debugging and improving the engine is another moment you could have been working on the game itself, because almost all engine improvements are orthogonal to improving the game experience. So given a limited amount of time, you will…
In my experience, it was easy... until I got to the part of my game that makes it unique. Then it went from easy to very very hard. That's the thing about engines. They'll get you up and running quickly for basic stuff, but you'll be tearing out your hair when you need to do anything non-basic.
This is one of the multitude of reasons that so many older game devs reach for the C++ compiler; they don't know what the game will need, but they do know they can make the necessary modifications to ship if they approach it bottom-up.