Because the MacBook isn’t particularly short on space. The MacBook neo appears to have massive blank space blocks where the speakers are.

The 3.5mm jack is fine, there isn’t any need to replace it on the MacBook where you can afford to have both. On the iPhone it makes more sense to use the usb c for audio.

That hasn't stopped them from periodic stalinist redesigns in an attempt to purge other ports from their machines. But the audio jack always survives.