You sound like you dont know anything about programming (at least engine programming). Most Engines have to run in something like assembly, else they would be too slow. (They use others too but Assembly is in like all, i am a junior dev so i could be wrong)
Assembly is already a large hurdle.
I mean it is “simple” as the arch linux type of “simple”. (Nothing more than you need to run it and nothing more)
So the option is to learn assembly or hire someone (or multiple) who can, good luck by finding one that is capable of developing an engine that does not suck and does not cost a fortune.
Then you need to know what the engine should do.
If you “only” need 2D or even only some system to interact with the console you will be fine, maybe.
3D is a bit more complicated, the reason why there are so much 2D/2,5D games out supports this claim.
Then particle support if you want it…
Every feature you want has to be supported!
And every feature costs and maybe needs maintenance when bugs occur. Supporting an operating system is a feature too :)
So the engine has to be updated when a mayor OS update comes out
There are more points for why not to make an own engine and use one of the marked that fits ones needs even if it is closed source.
You where so fond of Godot so trying to help them might be a good starting point for you to life your ideals. I sincerely dont want to mock you with the sentence. If you can successfully help a larger open source project everyone is happy. If you can learn something new i am sure it can benefit you. I was only a bit mad because it felt like you are comparing engines with “weekend projects” what they are definitely not in the slightest.