That is why they are considered as alternative coins to Bitcoin because Bitcoin is more volatile than and has more longevity than them which makes it more like a stable asset in terms of existence in the digital finance ecosystem. Altcoins have less volatility this means they fluctuate less compared to Bitcoin. If they drop in price it may take longer for them to recover becuase they are less volatile. And they also depend on the influence of Bitcoin for them to also rise back up whenever Bitcoin starts increasing or breaks a new ATH.
In crypto market only Bitcoin can be trusted for long term investment. The alt coins are good for short term but are risky. We are not sure that alt we are inveting will go up or not. There is also chance that the new alt may be adondnded by its team soom after the laucnh or it may even be a scam. These all risks must be kept in mind while investing in Alts. A safe bet for alts is to to chose top 20 alts from coinmrketcap and invest in them only. New alts are more risky for investment.