Volume is extremely low on most DEXes and I hardly use them except for some lesser-known tokens that I want to sell that are only listed on them. I don't use them because of low volume and also the fact that most DEXes have UIs that look like they were made by children (EtherDelta)- I'd much rather just use a traditional exchange for the 99% of times that I'm not trading an obscure token that's only listed on a DEX.
Besides that, most decentralized exchanges usually don't offer any major new features besides being decentralized over traditional exchanges, and coupled with everything I've mentioned earlier I can't be bothered to try them.
Not only that where DEX do only supports mostly on Erc20 tokens which do flood up on the market.I agree that DEX do have lesser volumes compared to those centralized exchangers.Most tokens would be mostly listed up here when they dont end up on being listed into better exchange or users do tend to trade it first thats why we cant really expect for volumes to be big similar into other exchange not dex.
The thing i do like with these exchange because it isnt centralized, no kyc or any other related stuffs.