Simply because they have no value, and you don't sell it anywhere. Some may sell but prices are too small for us to trade. So I think it's a reluctance to keep those altcoins in my wallet.
yes I agree, because the shitcoin has a very low value so it is forced to keep it in the wallet, if it can sell it sometimes the fee is higher than the price of the shitcoin so the best choice is to keep it as a display in the wallet, if altcoin has a high value, surely we will sell it but if it is low value and only becomes a shitcoin then there is no other choice and still have to hold it in the wallet