When the park put out a "register your interest" sign up for Hyperia coaster climbs, the response was huge. I've been made aware that if everyone who responded to that ended up actively choosing to do it, there would be a 4.5 year waiting list.
So a mixture of a high price, some form of pre-requirement plus needing an Annual Pass takes the potential load off of needing a waiting list, which would probably have been met with a worst reaction than what's currently happened. Maybe those 3 things were a little unnecessary, maybe the price is a tad too high, but the park put those measures in place to allow a smooth introduction to the VIP extra.
I expect that at some point, they'll loosen those prerequisites, and maybe tweak the price (in the mid-term future) so the jump between other climbs and Hyperia's is not quite so steep.
I also know they had some concerns that if people did Hyperia as their first climb, they might freak out, not be physically fit enough, etc. Seems a bit overkill given Blackpool don't require it for Big One, but I wonder if that's just Merlin's H&S at play