What ? If they are popular then why they dont have enough volume ?  That should be the opposite  . like for example binance got alot of volumes because binance is verry popular  . 

What you really mean to say is that decentralized exchange are not popular enough comapred to centralized ones because decentralized exchange mainly foccuses on altcoin and erc20 type coins  .  these kind of exchanges are seemlesly buggy and slow  .