If you think Platinum IV will increase every year then what you think could be right VIP Host will be more expensive may need Diamond Level to get VIP Host, they had already made this change a few years ago.
I agree with the other users above, Diamond level will be quite high requirement for a VIP host. They may apply a certain amount of wager requirement to every user who has a VIP host, the wagering will be needed to continue with the host on the next month. Stake has already hired a good number of hosts, and there are also a good number of Platinum IV+ users who doesn't wager anything significant for a long time. They can reduce the load from the host by applying wagering requirements every month.