If it was not for the adoption of their own M1, Apple could not have made it thin as it is with the new iMac.
The engineering difference between Intel's: hot, bothered, power hungry, fan spinners, wasted clock & instruction cycle software and laggy performance -
Compared to Apple's M1: cold, energy efficient, software matching snappy action, and no more spinning beach balls.
If you look at the new M1 circuit board and power supply requirements, they have considerably reduced in size and coupled with the low heat generation, they can now get thinner, lighter and trim than ever before.
A case in point: look at the circuit board size of the new M1 Mac Mini compared to the older Intel Mini board - it occupies less than half the case: