Are they new? I guess people still want centralised exchange. I see that because the number of traders on centralised exchanges are very huge in volume. Look at Poloniex. They are the most popular exchange for altcoin. Even though they are centralized. Maybe they feel more safe because they think the security is tough than decentralised exchange. Also, there's a lot of exchanges all over the which scams a lot of people. Maybe they are just taking precautions although decentralized exchange has a lot of advantage.
If you got scam by the traders or people who came for trade then you can use the escrows to have safest trade. These escrows will hold the payment and bitcoin for the both parties. If the exchanges site been centralized what would be advantages according to you? I do not think anything will change because of that. Don't consider this information, do trade with the decentralized exchange as well but trade it safely.