I do game development consulting now and then (speedrun mode, leaderboards, randomizers, supporting infrastructure, etc.) and it's really nice to see Godot mentioned here. I don't often make projects from scratch but it is genuinely a pleasure to use.

In regards to developing your own engine - it's almost never more efficient to do so nowadays, but it is almost always significantly more fun. If the author has enough wealth accumulated to quit their job and work on a passion project full time, I imagine they can afford to do something just for fun as the baseline.