I am not saying that what you are saying is not feasible, they would have to sit down and calculate how many more new people they can get and how much they would profit from it. But I feel like it may not work for them.
They had it at a bigger percentage when they begin offering the Wheel of Fortune spins but after sometime they decided to make changes to the system so the bigger of the base rewards would fall not often as it was the case in the beginning,I remember within 98 spins daily you could without a doubt win the biggest RP rewards,I am not saying that they should change it to the beginning as maybe you are right they tend to lose a lot of Satoshis this way but from my perspective they very well can as what they lose compared to what they earn from gamblers here is completely irrelevant in my opinion.