It takes just as long to buy an AMD based PC as an Intel one, ditto installing Windows, apps, etc. Other than creating a new master image with the required drivers I don't see what is different and you would need to do that for a new range of Intel based PCs anyway.
It's not more expensive to sell AMD PCs than Intel, but it is more expensive to have to sell BOTH, slightly different models.
For your home PC, you just put something together, and if it seems to work, you go. For big vendors, all their hardware gets extensively tested and certified as compatible with all the major software out there, and full compatibility in all the edge cases with all different possible (supported) combinations of hardware is tested as well.
Businesses that buy thousands of PCs from a vendor in a go don't expect to get something that works most of the time. If they want to stick a SCSI controller card next to high-end video card, it all has to work.
I remember my old PC Chips motherboard... If a case screw happened to make contact with the metal plating around the holes, the second IDE channel would freeze. Worked perfect out of the case on a bench for testing (as the seller told me when I returned it), but in a case, it would go wonky. Even with good, name brand gear, there's still all those edge cases where it doesn't always support every configuration somebody might try.