I am tend to lean more on the theory Stake and it's administration is not willing to implement a service for exchanging coins because if the legal implications it could mean for the platform, they are already one of the biggest casinos within the ecosystem of cryptocurrencies, so they really do not need to add such feature to catch more attention from gamblers.
One must keep in mind that because we are taking about a service which have a high volume of deposits and withdraws, international authorities have kept an eye on Stake because it would serve as s way to launder money, thrus the AML measure they keep in place to comply with law, if Stake started to function as an exchange as well, it would mean regulators closing in even more on the activities carry out by users and they could even take advantage of the opportunity to pressure Stake to ask for me KYC information for their gamblers, even to the point of asking by KYC during registration (the same way it is done on exchanges), that would turn some gamblers away who wish to deposit and play as soon as they create their account.

Regardless of that the their strategy in the long term is, I believe Stake does good by staying away from the exchange market, at least for now.