it is because of bitcoin that they exist not the other way around.
people go to altcoins in order to make more bitcoin and if anything that should decrease bitcoin price because people get much more bitcoin they used to have and if they sell price tanks.
bitcoin rises on its own and has nothing to do with altcoins other way is correct however. altcoins get dumped as bitcoin rises and they sometimes get pumped if bitcoin takes a temporary dip
and even if there weren't bitcoin would turn into something like gold. or are you going to say gold is valuable because i don't know iron exists!!
p.s. so far in past 7-8 years thousands of altcoins came and gone and there will be thousands more in the coming future and they will continue to serve one purpose only: to get pump and dumped
until something changes with people who create these coins.