The tournament is probably ran by the provider and not the site. This happens a a lot if not most of the time as it means the site can advertise the huge potential prize pot whilst potentially paying out nothing to players on the individual site.
Pragmatic Play ‘drops & wins’ tournaments are a prime example. Where the leader-board is shared between 100’s of sites including outside of the UK where bonus buys and turbo spins count towards the leader-board
Playtech do it with their progressive jackpots too where the bet size influences the potential chance of triggering a jackpot (it says this in the game info). But bet size is limited to £5 in UK and $500 outside….