To add to the sibling comments, it might be better to think of ARM less like intel, and more like lego for building processors. Standard kits with a sensible collections, but you can always just ask for the IP blocks and diy. If a vendor discovers something isn't working for their application, they can turn it off, build a core without it, tell the compiler not to use that feature set. It's very modular.

additionally: x86 grew up on devices that were basically always plugged in. ARM has a huge install base thats significantly power or heat constrained.