Because on 2017 bullrun people are too hype to buy bitcoin and altcoin thats a reason most altcoin make it all time high, but look at ripple (xrp) right now the price are continue to falling down because people are now learn there lesson not to make a single move so its hard to tell if ripple will repeat its all time last 2017 bull run.
when the bull and the decline thereafter and until now there has been an improvement does not already prove to us that all crypto assets will continue to move. although now the decline does not mean it will continue to happen. if there will be bulls in the future, of course, XRP will follow the pump.
The chances always open to any big supported alts to follow bitcoin once it start to pumped high, the bull will lift XRP and other top coins from CMC
when bitcoin value established a good barrier, diversions can be expected for traders who gains good amount of btc to start targetting known alts
that also have good communities behind.