Bisq is probably the most known decentralized exchange. Transactions counts :

BTC / EUR : 105 k

BTC / USD : 72 K

BTC / GBP : 18 K

AND

BTC / XMR : 41 K

BTC / ETH : 2 K

BTC / LTC : 0.3 K

BTC / ZEC : 0.2 K

Monero volume is around 20x ETH, 2x the GBP, 57 % of USD and around 40 % of EUR (the most traded), the real question is why ? Why Monero is so used ? I think because Monero is the only one that fulfill the original conception of electronic cash system by cypherpunks, not Bitcoin...