Because when new bull run will arrive there will be new shitcoins and your shitcoins will end dead or delisted from exchanges which can lead to 100% loss.History is always repeating.
5,5 years old chart:

Surprisingly some coins from this chart are up from then but volume on exchanges is low,so holders of these coins are truly bagholders.
The safest way is to hold a holding coin that has good popularity, because the risks we get will be very small. Usually the risk of coins that do not have popularity will have a huge risk. For beginners, buying popular coins is an option, but for someone who has experience to do analysis, buying a new coin can be a gamble. When appropriate, of course the benefits will be even greater. It all depends on the choices we make, we have a strategy and we must be able to choose according to our abilities.