eXch almost always has zero XMR reserves (like most exchanges) ... they have over 100 BTC in stock and not a single Monero ... maybe they don't care.
These numbers change frequently. For instance, right now there is over 650 XMR in their reserves. This can go to zero by the time I finish this post.
But from what I've seen, they have a very low price for XMR (considering the market), and coins sell out very quickly.
Their service fee for monero swaps is 5% to 5.5%. With other assets, the fee is 0.5% to 1%, so they charge much more for monero.