When you went to a casino for the very first time? What game did you gamble with? Most likely it was slots. The house edge is high however most people don't know that. Actually in most casinos there is an information page and it lists the house edge for various games and for slots it's the highest, however nobody actually reads this.
I think the reason why they are so successful is because it's very easy to play. Most people never gamble and never played cards or rolled a dice. With slots you don't really need to do anything after inserting your money, just pull the handle and if money starts pouring out of the bottom, you've won. If it doesn't then you lost.
I have been playing on a place with 5% and still had a lot of fun. So, in the end if slots are fun and entertaining (they so are by the way) then I don't care about a tiny uptick on the slots ones. However, if the stake team wants to drop that down, they could add a jackpot which would give everyone a chance to win a big jackpot once every 100 years that would make it all worthwhile and drop the rate of house edge on slots.