At first I was going to just copy/paste his article and call it my own then I realized that is kind of a dick move.
How to make your own game engine (and why) by Tyler Glaiel
Well worth a read.
In my 35+ year career in games I’ve never used an off the shelf game engine. Starting with SCUMM I’ve always build my own. I love the power and the freedom. It’s hard work and probably cost me more but I love making game engines and writing compilers. It’s a skill you slowly acquire and after the 5th one it’s not a daunting task anymore.
I ran into a programmer at an indie meet-up and she told me this story about how another programmer at her company brought up building their own game engine. Someone responded with “What! Are you Ron Gilbert!”
I wear that as a badge of honor. :-)