I have worked briefly in the game industry long ago (not in engine teams though) and ended up writing a few engines for myself after leaving, a couple quite complete.
It’s just a hobby like another. I have zero interest in writing a full game on top of it, or even publishing it.
But do you know who NEVER gives me grief about it? People I know who work at Unity or [previous employer] writing AAA engines.
My last monstrosity is a Rust one with zero dependencies other than the std-lib/OS, Metal/DX12/Vulkan, its own physics engine, spatial audio, vm for scripting and other stuff. I will probably do nothing with it other than having updated my skills in a lot of areas.
Once I tried to create my own front-end framework from scratch. I created signal library, mounting/unmouting, context etc but never able to write v-dom diffing or using existing vdom libraries.
Then I decided just implement my API on top of Preact. Preact did vdom-diffing for me and mounting/unmounting which was enough for my need.
The final project looked nothing like Preact, it even had it's own context system, data loading, signals, setup + render and context which just hooks itself into Preact Context but taught me a lot about how a front-end framework work.
That said, it's still a worthwhile exercise that one can learn a lot from.
Do we want money or do we want to get the pleasure of being an engineer and make money as a side quest?
There was a video of tsoding about why he doesn't have a job, he says "when I have enough money for my needs I just go into coding instead of working". I like his vision. He likes coding for the sake of programming and earns money as a side quest.
I wanted to make a game, and had an idea, but then I thought "why not making a game framework so I make my game". It was fun to build a game framework by mixing PixiJS, Rapier2D, ECS, writing my own loop logic and state management but then I lost the motivation. I just coded a framework for pleasure but at the start my point was making a game.
The desire to build something can cause our idea to be dropped.
IF you want to make a game engine, building one is progress
If you want to make a game, building a game engine is the illusion of progress. When you're done making the engine you'll be no further along on your game than if you'd used an existing engine. Usually you'll be behind because those other engines have so many features and tools that you have yet to implement. Sure, you don't need every feature, but you may be surprised at all of the little things you end up having to write.
Starting from a checklist of features for a game engine almost always ends in wasted effort