Im just puzzled why BPW wouldn't lay on another bus. They must have enough drivers, maybe they don't want too many people on the trails in this weather, but that's what all weather surfaces are for.
IIRC it's more that they are restricted in how much traffic they can sensibly put on the forest access roads, if you've been on the uplift you'll notice they are only able to pass one another at a few points. in good weather they were getting a Van away form the pickup point every 5-10 min's or so (Running 3 or 4). I did talk to the Drivers and running more than four busses at once just makes the logistics a bit more complicated, and probably won't improve turnaround times hugely, I think they do run reduced number during the week and then lay on more capacity on the weekends to fit peaks in demand.
And of course Vans ain't free, if they buy another one, it's got to be able to pay its way, they don't want "over capacity" it just dents profits, and it is a business after all.
From a profitability point of view it's better for BPW to have more Demand than Supply, if they can pretty much guarantee high/full occupancy and full bookings months in advance (especially when the weather is shite) then they are not going to be throwing away money, laying on extra seats for people who don't actually want to come.
Laying on more busses would probably mean investing in upgrades/changes to the access routes, not the trails... I'm sure they have a plan, but there is a limit to how many bodies and bikes you can sensibly shift up and down the hill.
Personally Next time I visit I just plan to take my HT and maybe a little change in case the vans have a spare seat, but I want to pedal up as much as I can manage, makes me feel like less of a Nancy...