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.
They have the lowest prices on the market for large purchases. The fee is negligible. Try buying such quantities elsewhere without KYC, you will pay much more.
They probably have a philosophy that holding Monero is inappropriate, considering the possible sharp drop in price upon delisting.