> they don't sell their fab capacity.

There is a "fabless" division of Intel that uses their fab to do designs for third parties. You won't hear much about it because a) it's for relatively niche stuff and b) it's historically very uncompetitive in terms of IP offering and schedules. So nobody uses it. Every so often they try and re-invent it, a few years backs they were pitching the Altera aquistion as a benefit but so far it's remained uninteresting. Being able to offer capacity might change things for some prospective customers.

But AMD compete with intel, and consumers might look at nm size when comparing mainstream processors to buy, because at one point it was a good indication of how recent the processor was, and thus how fast / power efficient / ...

Not that I'm not talking about educated consumers, which will look at other variables, but rather the consumers who will buy a computer and want the cutting edge, without knowing too much details.