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.
Out of that Image i do only recognize Rank 1 and 2. BTC and LTC and the rest i dont know whats the situation of those projects.We do compare the ranking as
of this moment and to the image above. We have seen that most of them failed and even the current ones would still have the tendency to to rank down and would be replaced by newer
ones.For the question on holding shitcoins will make you rich then theres a possibility but the odds would really be like betting on a lottery.