Actually they do over drive them. I think it is explained in the asahi sound driver GitHub which reverse engineered the Apple driver.

IIRC, there is an algorithm which overdrives the speakers in physically dangerous zones only on some frequencies and only in short bursts of time with a throttle until the next over drive if necessary.

For the user it’s transparent because we are talking about timings in milliseconds so except if you play a static frequency you can’t notice anything.

Asahi explained that they had to reverse engineer this because they didn’t understand why the sound was so bad on Linux.