I think there Rollbots and other casino perks is what makes them rewarding and not the RTP for each game because it was set by the provider and not the casino.
This is what a lot of people think but it's just not true.
For instance Sweet Bonanza:
Roobet: 95.5% RTP
Stake 96.6% RTP
Rollbit 96.6% RTP (effective RTP with rewards 98.6%)
So at least Roobet has lowered their RTP from what Pragmatic normally is.