ASUS definitely still makes several motherboards with PS/2 ports. My Prime X370 Pro has one, and the updated X470 version still has it. The Prime B350M even has separate ones instead of the combo.
AMD's overall marketshare is still low because of near-zero laptop or OEM penetration but their share of retail CPU sales (i.e. the only people that buy motherboards) is nearly 50% according to every recent sales report I've seen.
ASUS has literally dozens of current motherboards with PS/2 ports, including 5 Z370 models. I really have no idea where you get the idea that they "dropped it completely".
Despite Ryzen AMD is still negligible as far as market share goes.