Shouldn't there be some anti-trust limitation on that?
Natural monopolies are not illegal and Apple is selling hundreds of millions of devices that use these chips every year. Apple silicon is in every Apple Watch, Apple TV, iPhone, iPad, Macs of all sizes (soon), headphones, and so on.
Placing limitations on a single company itself would be anti-competitive because we'd be restricting natural monopolies from growing and placing favoritism on other competitors, which itself wouldn't be fair either.
Wouldn't Apple customers suffer just as well because they can't get Apple Silicon SoC due to supply restrictions enforced on them?
Apple isn't stocking chips to prevent others from taking over, they're buying every supply they can to ensure they have enough to sell all year long and they're planning several years in advance.
Put it another way, if AMD was richer years ago, AMD would be doing the same thing to get larger share.
There's nothing stopping AMD and others paying TMSC several tens of billions of dollars to build a fab for them.
Also, let's remember that AMD had their own fab but sold it off (GlobalFoundries).
Like imagine not regulating a natural monopoly that provides electricity. They'll serve only areas they want and will not serve the rest. Good idea? Nope. Requiring them to serve areas equally is a proper method exactly because it's a natural monopoly.