There isn't really a use-case for a fundamentally new OS. There isn't a particular need that's going unmet by the big three, and the existing base of applications and driver support on Linux/mac/windows is vast and extremely mature.
It's like saying why hasn't anyone invented a fundamentally new class of road vehicle that isn't a car, truck, bus or motorbike, using entirely separate roads, infrastructure and fuel? Do we have a sudden shortage of inventors and engineers?
Well, no. No we don't. I'm sure someone could come up with an absolutely delightful monowheel gyroflivver, and it would be all kinds of creative and neat.
But if it won't fit in anyone's garage, can't share existing roads, needs a while network of clockwork-winding stations and can only carry your stuff in specially-shaped tow-pods you have to buy separately ... then nobody's going to use that to get to work, or go shopping, or wherever the hell do with cars I don't have one idk - so only three people will ever buy one, and there'll never be any infrastructure for them.
Corporations rely on desperate, easily-exploited people in order to make obscene profits. There's no way in hell they'd risk actually cutting off their supply of slaves, or else they might have to drop a couple of percent of profits on paying wages / benefits / etc.
The border laws aren't intended to reduce the number of illegal immigrants, they're there to make those same people more desperate and therefore more profitable, while at the same time stoking the enthusiasm of morons who will continue to vote for more pro-corporate politicians who will shovel even more money to the shareholders.