Of course if someone wants to gamble in the currency he got it's no problem. The point is that when you want to implement multiple currencies this means you got a lot more effort maintaining those currencies.
They can still implement other currencies but if they have implemented Coinswitch they can also attract players with currencies they don't support.
Also when you use something like coinswitch that makes managing the currencies a lot easier as well, other option of actually adding it to the websites core means that wolf.bet would have to have a node that they run in each coin they have so that they could pass all the things they do through that node to make it easier and have a whole wallet system that they use to allow people etc etc, basically a very long and hard process that takes a lot of time. Whereas coinswitch allows you to do this with one click, they handle all of this, and wolf.bet just pays a commission to them and be down with the whole situation.
This is why adding coinswitch makes a lot more sense. I had coinpayments on my website for example, had like 200+ coins easily, only use 5-10 coins myself, but it allowed me to accept a lot more coins than I was using at the time, same logic here as well.