If you had a large amount of cryptocurrency would you prefer to keep it on an offline cold wallet or an online cryptocurrency exchange?
Cold wallets should not be compared with exchanges, this are two totally different things.
You should never keep anything on centralized exchanges long term, and if you do this you have to know that this are not really your coins because you don't own the keys.
Only trader would have some excuse if they are trading all the time, but they should never trade with all their coins.