You have to push off the skateboard or skates to move. A lot of the force would be used to compress the springs so the effort required would be much more.
Also I think that there would be some amount of rebound if you try any tricks and again effort would be required to compensate for it and even then the results would be less than desirable.
Btw skates, rollerblades and skateboards already have shock absorbers and we call them knees.
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