reason is because some people find it difficult to move their old token to a new wallet that's those people who started using trust wallet since 2018 i think is only those old users that is facing this difficulties.
If you are using a wallet that does not let you move your coins when you want to, then you should ditch that wallet immediately for a better option, no matter how long you have held your funds in a non custodial wallet, you should be able to spend it whenever you choose. I have not heard of this problem you are talking about with trust wallet anyway, but irrespective of that, it is advisable not to use trust wallet to keep your coins, particularly when it is Bitcoin you are storing, for shitcoins, maybe!