No one mean harm on them but they impose more danger than the benefits they offer, so many crypto projects have crashed down in the past and renders investors in penury of argony loosing their assets, anything that can be traced, hacked and attacked is unsafe enough to go with because the risk in there is high, people aren't scared about the centralized exchanges but fear loosing their entire investment on them.


The danger lies on the type of exchange you're using, we have a centralized exchange that has the custody of your wallet keys in their possession and such examples are the likes of hot wallet, mobile wallet etc. The second type is the decentralized exchange, which gives you access to your keys.