RPS is very easy to make provably fair. In fact I do it all the time. Here's a good example of me playing in a provably fair way (for both of us) just using this forum:
https://bitcointalk.org/index.php?topic=1588904.0 and includes a lot of explanation of how it works
I didn't know RPS could be provably fair, that makes things a lot easier to add in a game. I would really love to make a website with provably fair RPS in it, you wouldn't need any bankroll at all, just make people gamble against each other in a provably fair method and you would make money from rake instead of spending any money yourself.
However, there would be development+design+marketing costs and as a person who has less than 5k dollars in bank account all I can offer would be cheap third world development+design and wouldn't be a good job done for that amount of money and on top of that I wouldn't have enough to market it.
People think when you can code a casino the job is done, that is literally just step one of creating a website bustabit didn't became bustabit in one day.
We've actually got a RPS mode on our site releasing soon.
However we're still considering the best way to approach it, as it's only truly Provably fair for the joiner, not the creator.
In theory the casino could still know what side to chose if someone were to make a game, the only way to combat this is having the user submit the hash themselves.
So you're sacrificing user experience and introducing a lot of human error into the mix, versus just having a warning that states it's only provably fair for the joiner, not the creator of the game.