Well, it depends on the person who's doing that. Maybe keeping a token on their wallet already became their hobby instead of using it for trade. As for me sometimes I am hodling tokens depends on the usage of it or when I belive it will have good future. If not I prefer to buy and sell instead and taking profits from it.
if it has value then it is useless, usually they keep tokens that have no value, because how are they sold ?, sure will not sell,
I am an airdrop hunter, and I experienced that, many tokens in my wallet now and only become a display in my wallet