....
Because stupid people who bought the original W140 S Class kept breaking the electrically positioned one by manually forcing it rather than using the convenient switch. So for the face-lift, they deleted it. Permanently.
Someone at Mercedes should have bought an Omega to see how it should have worked then
Mercedes engineers weren't the problem...
It was more to do with the customers, or their wives, who never bothered Please read the manual
Trouble is, being fully motorised meant the mechanism was really weak so didn't take long to break when people went to adjust them by hand, making them all floppy.
The easiest solution was clearly to delete the function rather than trying to educate the owners... The cost of which would probably have doubled the car's not insignificant development costs