you're not the only one. jonathan blow has made tons of money selling games and also needs to write a whole programming language for 100h to keep him interested enough to yield 1h of content.
i can't really say much about the people who say don't program game engines (or whatever thing they don't like) in terms of opportunity costs (a generous name for this category of complaining), other than they would be bad at both making art and making money.
What a ridiculous take. Making a game engine is to games like building a camera is to making movies. Once a blue moon some new camera enables some new technique (the Matirx), but mostly people just use the tools that exist.
The same is true in games. Tons of super popular and successful games didn't write their own game engine and made both art and money.
I'm watching a friend, claiming he wants to make a game company, burn through all of this money instead making a game engine. If he succeeds, great! But I suspect he'll just run out of money before he's even started working on a game. If it was fun to make, great too. But I think he'll look back on it as throwing away an oppotunity.
Been there, done that, didn't regret a thing since i'm certain i'd have given up way earlier (assuming i'd ever bother starting) if i had to use an existing engine :-P.
(ok, i never had money to "make a game company", the most money i ever had was to be able to spend ~2 years living frugally while making my own stuff, but it is close enough since i think someone could say i should have used some existing engine instead - which is true, except i'd hate doing that)
There are people who want to make games, people who want to make engines and, perhaps a minority, people who want to make games and engines :-P.
(though FWIW in my case i never felt the tech side was much of a limitation, it is art/content that ends up being the bottleneck and makes everything crawl down and the stuff i like to do aren't the kind of stuff you could do with procgen, minimalistic styles or other similar approaches for saving on the art/content side)