The thing is, when you only have one or two competitors, you're really, really careful not to ruin them. Otherwise you'd become a monopoly and subject to all sorts of extra attention. It's less of hassle to keep them around.
No company wants to be a monopolist, unless being owned by the government. Being a monopolist sucks and makes the whole business much more expensive. Not to mention the state would do everything possible to divide such a company anyway.
For Intel it's way more convenient to give AMD their 10% market share - especially if it's not a very interesting part (like HEDT).
We have to wait until AMD gets competitive in mobile solutions, to actually see Intel giving a f...