I don’t know why you’re getting downvoted. It’s a fair question to ask.

“Why can’t I buy” is essentially equivalent to “why doesn’t anyone sell”, which is basically “why isn’t there a market for?”

It’s possible to have a conversation around “why isn’t there a market for ARM desktops?” or equivalent but a conversation about “why isn’t there a market for anything but x86” would basically be enumerating the alternatives and examining each.

Nobody is going to open a store aimed at the “anyone but x86” market.