1 - imagine there was NO give at all and you went over a pothole... the top would shoot out the mount
2 - expense/size
3 - if you could lighten the front end of a car to the same weight of a couple of subbies and an amp then that would be a good idea maybe, but you cant
4 - turbulence issues.. but i am quite uneducated in this exacty
5 - Moved to general automotive discussion