Hard Tail Knockoff Why Are Hard Tail Mountain Bikes Faster Than Full Suspention?

Why are hard tail mountain bikes faster than full suspention? - hard tail knockoff

I think the purchase of a hard tail or full suspension mountain bike. I read that the suspension has been slower, but I wonder why, because I probely few races mountain bikes. I also wonder whether there is a proposal on a bicycle. I am 13 years old and weighs 90 kg and 5 meters high, with a limit of $ 900.