>>714455864 (OP)many reasons
they used to use off the shelf parts, now everything is custom
metal has virtually no support compared to directx and vulkan, requires rewriting a lot of shit for an audience that isn't there
even their best chip can't hope to compete in raw rasterization perf compared to a 4070
apple restricts low-level access to hardware
it's not all bad though, they excel at running MMO's due to them being mostly CPU bound and games like WoW, Runelite and FF14 all having native support