That's not really true. EPYC doesn't share silicon with any of the mobile Ryzen products. AMD has, at least in the past, been financially limited in what risks they want to take with their new Zen-based designs. You are correct in asserting that the highest margins are in the server market, which is why AMD prioritized their entire design effort towards server/workstation products (EPYC). Lower-margin, high-volume efforts (mobile, low-power) get short shrift. That's been the case up through Renoir. Renoir's adoption appears to have been quite enthusiastic, though, and if OEMs are privately asking AMD to bring Zen3 to the mobile market as quickly as possible, then maybe AMD will reprioritize development efforts.