Because as you play some of the games, it builds up a meter that can trigger the bonus. This meter stays at the level you have built during each session. So when they changed provider this progress was reset to 0.
so here is just another complaint about not winning a potential bonus. I believe that everyone knows that bonuses are not an obligation of any casino, and they create them at will and cancel them when they want or think they are no longer needed.
OP, unfortunately for you, there are no elements of fraud here. you can only pretend that this casino is not fair and they don't have bonuses worth paying attention to.
Just check their trust history and you wouldnt be surprised their activity if they screw up with the dealings with an affiliate, I wouldnt be surprised if they also wont give a shit about their customer.