They literally can't. They moved the headphone jack from the back to the side because it was too long.
Now you could argue if it needs to be that thin but for the current configuration, there's nothing you can cram behind the screen.
Now you could argue if it needs to be that thin but for the current configuration, there's nothing you can cram behind the screen.
They can't put the compute in the back of the display itself, while maintaining the same thickness like an iPad (which has the same CPU), because the room behind the displays is dominated by the speaker system, allowing the iMac to have surprisingly good audio quality despite being so thin.
[1] https://www.ifixit.com/Teardown/iMac+M1+24-Inch+Teardown/142...