I'm sure HP and Dell would sell you a Ryzen box if they thought it was profitable.
I take it that you missed Intel sucessfully locking AMD out of the market when the Athlon64 and Opetron completely blew away the P4 and Xeon's of the time?
El Reg covered this quite nicely back then:-
This also summerises quite nicely.
Intel’s illegal conduct was two-fold: firstly, giving rebates to computer manufacturers — Dell, HP, NEC and Lenovo — if they bought all, or almost all, of their processors from Intel. This was also combined with direct payments to a German retailer Media Saturn Holding for stocking only Intel products.
Secondly, Intel paid HP, Acer and Lenovo to limit or delay rival AMD-equipped products and squeeze them out of sales channels, the commission found.
Personally, I doubt that the same retailers not selling anything from AMD this time around is down to the merits of the product.