Because the competition in the ARM mobile/SoC vendor area is thin. There are Samsung, Qualcomm and Mediatek plus a few underdogs no one cares about (Nvidia, Intel). Apple is no competition as they don't sell to outsiders which means there is no competitive pressure to improve. Look at the utter shit that Mediatek dares to sell (ever looked at one of their BSPs? I'm surprised there are not daily CVEs!) and yet they're highly profitable.

Plus, AWS/Google are also actively gobbling up silicon design talent to fight Intel and AMD on the server area, which is a problem as designing powerful server cores is way easier than designing SoCs for mobile devices.