> Genuinely asking -- what is it due to?

Mostly memory/cache subsystem.

Apple was willing to spend a lot of transistors on cache because they were optimizing the chips purely for mobile and can bury the extra cost in their expensive end products.

You will note that after the initial wins from putting stonking amounts of cache and memory bandwidth in place, Apple has not had any significant performance jump beyond the technology node improvements.

I still don't understand though. Given their profit margins, the fact that they're shipping m chips in eg $1k computers means it's a $150 part.

There's tons of people that would pay $300+ for an equivalent perf + heat x86 competitor.

They aren't aiming for performance in the first place. It's a coincidence that it has good performance. They're aiming for high performance/power ratios.

Wasn’t the M3 a reasonable increase and the M4 much more significant than that?

The M2 was certainly nothing amazing in jump.