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.
Surprisingly some coins from this chart are up from then but volume on exchanges is low,so holders of these coins are truly bagholders.
Yes, coins like namecoin, peercoin, devcoin aren't even in picture now. Namecoin is now ranked 230.
Even good project LTC is no more in position no. 2. So, it is always good to flip your alts and stay in BTC.