I seriously doubt there are millions of WSM rifles in the hands of American shooters. That doesn't keep them from feeding just fine. Most bolt actions don't have the problem, controlled feed or not.
Semi-autos are a completely different breed. Dynamic feeding presents lots of problems, first and foremost the magazine has to present the cartridge at the right time and position for the bolt head to strip it out, push it forward, and chamber it. That is a situation that has to be fine tuned regardless of caliber.
Introducing a oversized bolt head to handle the cartridge adds another technical issue, especially in the AR platform. Go too big and it weakens the bolt. There is only so much room to enlarge it, and the larger bolt head takes up space where the magazine might sit, plus the barrel extension has a limited amount of room. Making the locking lugs bigger is a real problem in a restricted space.
The Russian case so many wildcats use, like the .264 LBC, is already pushing the limits of AR design. Hence the marketing of the alloy superbolts that resist pressures better. It boils down to the fact that you can't just shove in a big cartridge into an intermediate caliber without taking into account a lot of other factors. And since the WSM's are a niche market, there's really not enough cash loose to spend on developing an odd combination.
Millions of rifles would include the .30-30, .30-06, .308, .270, etc. WSM's aren't common at all in comparison.