It's really a trend now that casino's has to make their integrate exchange, it's up to them if they will tied up with an establish exchange or they can create their own brand for their users.
Creating your own exchange brands add more responsabilities, and more fronts to cover (security, promotion, legalities, etc). If you just want to provide players a better and easier way to bet, and nothing more, then the exclusive exchange is going overboard.
It is really not a needed responsibility and work for primedice to add in their own exchange, it is just totally useless when you can use coinswitch, I mean think about it having an exchange means you will have to build a whole new business on top of your current business, that is both too much responsibility and also so many much more work to do and constant expense.
At the end of the day they would have to charge you trading fee in order to cover the expense of running an exchange which would make no sense since they are already making money with the gambling side of things so why should they also try to build the exchange business to a profitable point ? I would say using something like coinswitch is already the best option they have and definitely worth it.