First time poster here. I work in telly, but nothing like GW.
I have some sympathy for the TV presenters who wouldn't go to those gardens. The presenters are paid to be there to do GW, it's all they're there for and if they mess up on GW, they've failed. There's a lot of time pressure on that team there; GW normally has more than a week for editing between filming and transmission, but at Malvern it's just a day or two. That means the pressure on all concerned is far greater and a presenter going AWOL can make a big mess of the whole show. And the presenters have a lot to deal with on days like that; scripting on the hoof, unfamiliar surroundings, an actual audience as well as the imagined one on the far side of the lens. I understand totally if they don't feel able to take on any more; they're under big pressure.
Also - and I ought to say I've never met and don't know any of the GW presenters - some people who are communicative, outgoing people on TV are actually quite shy people who hate talking to crowds, hate having to be "on show" and won't do anything public without a lot of preparation. I have a lot of sympathy with them; I know a lot of presenters across various genres, some are gregarious and outgoing, some are tremendously awkward, some are great off the cuff, some can't cope without a script. They're hired because they have the rare, difficult knack of being able to communicate through that strange glass eye on the front of a camera; don't assume they can turn it on at will to a group of strangers.
Oh, and they probably earn a lot less than most of you think. (Still more than us producers....).