I think a big chunk of that is power thermals -- Apple's ARM chips are only used currently in passively-cooled, handheld, power-restricted chassis (phones & tablets). Intel's chips are generally actively cooled and run on mains power, so they can run hotter and draw more power, so they can make up the difference by stuffing more hot cores onto the chip compared to what Apple has been doing.

Easy answer: Intel chips have more cores than Apple ARM chips.

But if they have the same number of cores it's generally a power tradeoff. A 12W chip can give 12W to one core or 3W to 4 cores. Transistors are optimized for a particular voltage & current, so when they run at a different power, performance scaling is not linear.

The funny thing is, the main selling point for intel processors for me was their better single thread performance over AMD chips and now Apple comes up with a faster single thread performance chip. I might get an ARM Macbook when they are in sale after all.

Heterogeneous Multi-Core Processing. 2 big cores. 4 small cores. Meanwhile Intel CPUs have 6 big cores.

Imagine two football teams.

One full of excellent prima donna's who don't work together at all.

The other full of good players who work really well as a team, communicate well and get out of each others way.

Who would you bet on winning?