Because Bitcoin gives a chance for more people to be rich. All cryptocurrency is closely connected with bitcoin.
maybe because this is the mainstream of all coins. if the bitcoin has only a low price I don't think it fit to be the leader of all coins. althoug there are many ivestors and users of the bitcoin if it only have an low price I don't think the other coins accept it. and also this is the firat of all cryptocurrency so I think it wiuld have a high price.