How would x86-64 be as efficient with the same transistor & power budget when they have to run an extra decoder and ring within that budget? Seems physically impossible.
Some don't, but a phone does.
Google has purged 32-bit apps from the official Android app store, but as I understand it the Chinese OEMs that ship un-Googled AOSP ROMs with their own app stores haven't been as aggressive about moving to 64-bit.
M1 has 16 billion of them
AMD is below 10 billion
it's not that expensive
it's a tradeoff, you lose something there, you gain somewhere else.
x86 has a more complex decoder exactly because it was less powerful and had to save on computing power and energy consumption, not being a mainframe.