I don't think casinos are deliberately manipulating things on their platform, or they're doing it whenever they feel like it. The house edge is implemented so as to give an advantage to the casino over the players in the long run.
Nowadays, maybe not so much, but in the past, there were a lot more online casinos that weren't provably fair. So, it wasn't just the house's advantage but there's always the chance that casino could screw you out of a good hand if they wanted to. And no one would ever be the wiser about it. You wouldn't know if they were doing something that would tip the odds in their favor.