too big of a project, too much risk involved
the companies capable of doing it aren't willing to take the risks, things like kingdom come deliverance are flukes
But that Kingdom Come game isn't even close to an Elder Scrolls "be who you want, do what you want" type of game. ELEX is even larger map-wise and arguably more interesting than Skyrim's map, yet it was made by a small fraction of what Bethesda's resources are. Had Kingdom Come not had a voiced protagonist and was set in a world with magic and monsters it would have done much better. It was a niche title from the start.
Until someone takes the risk and makes something like ELEX in first-person or a smaller but still large open-world RPG to try at the Elder Scrolls style, Bethesda is just cruising being the only option on the market. And they are a good option, but I'd like to see more. Certainly something can be done. Sacrifice some scale, scope, graphics and so on, and just work on making the gameplay and RPG stuff immaculate. PB also did it with the Gothic games, so how do they produce such magic while other medium to small sized devs don't even try?
And money and investment can be procured if the game looks promising. The Outer Worlds is a start but it probably will be much smaller in scope. Someone can do a Kickstarter if they have a working demo of the game or look for private investors like KC:D did, except don't make such a super niche title like those devs did.