> $50B for Micron.

$50B for Micron to build two fabs on the same site, i.e. they're still $25B each.

> They don't have in-house expertise to do that.

This is a questionable assertion to begin with. The skillset for designing logic and fabricating it are closely related enough that companies -- including AMD -- have traditionally done both, and companies like Intel and Samsung still do.

But more than that, what if they don't? You're not going to reassign your existing staff who are already doing necessary work anyway, you're going to hire new people.