It is just a difference in game design. Play n go games are not actually capped to the max win they say is possible. For example book of dead says max win 5000x, but you can get bigger than that. Legacy of dead also says 5000x max win, but I have won 6100x on it.
For example Moon princess 100 says Maxwin 15000x, and that is probably near the biggest they have seen simulating 100 billion game rounds. Have personally got a few 4000-5000x on that game, maybe some day more.
It is exactly as OP states, some games have "max win sequences" built in them, meaning the bonus rounds are predetermined. They make the logics of the games so complex that I understand the need for making them predetermined and capping the max win. Play n go bonus rounds are not predetermined and that is what I like about them, even though it is also awesome to get a max win round on gates of Olympus where it keeps bombarding 100x-500x multipliers on the screen.
In the end it doesn't really matter, I prefer Play n go style and you can prefer the more scripted style of bonus from other providers, to each their own