Here’s a genuine attempt to offer an explanation:
The geometry of the Five is pretty sorted. It’s been a good deal lower in the BB and slacker in the HA than most bikes until just recently. The low BB in particular mean is flies along and down.
It’s got just the right amount of suspension for UK riding (and hasn’t ever had too much or too little even when a lot of mainstream trail bikes were heading up to 160mm) and crucially that’s meant you’ve been able to run it with a 140mm 32mm stanchion fork which keeps the weight down to a reasonable c.28lbs.
It is simple in design and it’s British.
It’s bigger travel stablemate, the 223/224 has had enormous success on the race scene, especially in the hands of everyone’s hero Steve Peat.
A lot of very (very) good riders like it and eulogise about it because they get all the benefits of its design (slack HA, low BB, simplicity of design, goes down hill real fast) without any of the major issues of the design, i.e. the rear doesn’t work when you use the brake.
The better the rider, the less this issue of the rear jacking under braking is an issue; really good riders don’t tend to brake as much as us average joes.
I also think a big part of it is marketing; the marketing is very clever though. It doesn’t matter how good or bad you are on a bike, no one ever took the piss out of you for riding an Orange Five. You could be really joe average or ‘god on a bike’ and if you’re on an Orange Five it’s absolutely fine. It’s a bike for all people.
Whereas if you’re on something like an Intense, Santa Cruz, Yeti or other exotic, semi-exotic bike, especially if it’s a longer travel model, then you better be pretty good otherwise everyone’s going to point at you and say ‘all the gear…….’ I think that puts off a lot of people.