Retail PC sales are only a small portion of the x86 market. The vast majority of corporate PCs will continue to use x86 in the foreseeable future for compatibility reasons. On the datacenter / cloud side providers are trying to make inroads with ARM, such as Amazon's Graviton, but are meeting similar resistance.

Additionally we have yet to see x86 on the TSMC 5nm process. Making that leap once Apple's reservations expire may remove much of the performance gap.