I doubt it is about money at this point since he has been streaming under Roobet affiliate exclusively, so maybe someone can explain what is going on lately.
Its always about money and thats how they make their own living through gambling stream, why would you guys even expect gambling streamer to be loyal to only one site though? They can literally choose whatever sites that suits ( pay ) them the most. Anyway its either the 'other' site ( Stake ) gave him a better deal or probably Roobet stopped hiring him as their exclusive streamer but its probably the former.
That is what they do steaming for and is most important part of any deal which is money involvement and you could see once they reach certain level of audience reach on their channel the casinos strike deal with them to increase their userbase through them and pay them for the same.The deal could have certain time limit also and maybe that was over but other reasons are like you mentioned getting paid well from another casino and they switched to that streaming so not a Big issue at all.You still have to play in your own way and they will be doing streams of gambling for different casinos with time.