It depends a bit on demographics, but most casino players I know switch around. Now, some have several casinos they visit frequently. Many, many follow the bonuses. And that is getting to be a problem in Poker too.
The bonus situation has really ruined loyalty – if I were running a casino I’d take the risk and very gradually change my promotions so that bonuses are awarded after a certain amount of play. That would still mean you have a “wagering requirement”, but the player is not aware of it, and if s/he wins something, they will be able to withdraw it. There are casinos with nice loyalty programs, but players are trained to think bonus. I would start with a “split bonus” – the first half has a WR, the second is given after a certain amount of play and does not. It’s just words, but you need to use the words people are conditioned to go after.
Rake back is in a way a loyalty bonus. There is nothing wrong with it except that the poker room should be in control of loyalty rewards, not he affiliate.
The casino industry has been through the mess of affiliate incentivized play, and now poker is making the same mistake. It will resolve itself as more and more poker rooms will stop affiliate driven rake back. I will yet get to say “I told you so”.
So, as long as players follow purchase bonuses instead of loyalty bonuses you will see a lot of migration.
So you need to give players a reason to come back to your site. There is nothing you can do about the bonus mess, so you just have to position yourself so that you will be the only affiliate that player uses. Finding a reason for the player to do that without incentivization is part of the art.