I think the market positions can be explained much more easily just using basic market facts; technology doesn’t go into it.
Unity had a head start of several years for the “free to try” tier. Of course it has a bigger market among the people who don’t have a lot of money to spend right now.
Another measurement might be “how much money total do the games on the platform make?” and if that’s it, Unreal might actually be ahead, because of its AAA pay-for roots.
Unreal Engine is currently actually easier/cheaper to get started with for many developers, so it has that going for it.