No, you can trade crypto on a decentralized exchange like a token trading contract on ethereum. You do have the risk of bugs in the code or poorly coded contracts with backdoor but the code is public.
Backdoors aren't poorly coded, they are well coded but malicious.
You can but what % are on those? Less than 1?
Probably most of the ones exchanging fiat for cryptocurrency. But you can use defi if you want to swap crypto for crypto, and you can always send direct to buy something, although most merchants probably immediately convert to fiat using an exchange.
No, decentralized exchanges have had more volume and liquidity than centralized exchanges for 2 years.
Cuz of NFTs?
Not because of NFTs, people that chose to learn how to use crypto natively find it easier, faster and less of a hassle, than the people that chose to say these are insurmountable barriers to adoption and stick with those custodial exchanges
Just like with general computer use, after a certain point people can’t blame the user experience on their own incompetence