Even though Altcoins cannot mimic what they did during the late 2017 they are still somehow mirroring Bitcoin's movements the only difference is they aren't as high or as near in their ATHs when they are moving along with Bitcoin. The only thing I see why the bear market that was triggered after the 2017 bull run cause some kind of FUD that made a lot of demand go away from Altcoins
The top alt coin might mimic the bitcoin to a certain point but still i am not expecting some of the coins touching their previous all time high valuation as the situation is not the same and you cannot expect investors pouring in big amounts when the economy is going down and with the pandemic i doubt whether we will see a bitcoin rally like we used to see in the past, there are many variables that cannot be explained.