If HPV riders want sponsorship and recognition, perhaps they should be riding the Tour, Milan San Remo, the Tour of Flanders etc. Similarly HPV builders should try and get world level riders to ride their vehicles.
I think you'll find there's a good (or, perhaps more accurately, bad) reason they don't...
Obviously I meant using the appropriate bikes for the event, ie conventional bikes in (UCI) road races, and HPVs in HPV races and records.
Just speculating here, but regardless of a riders professional status, I wonder how transferable those skills are from one discipline to another. So often, as we all know in our own limited way, you've got to kind of immerse yourself in the activity and train specifically for whatever event you're taking part in. And one of the obvious differences with HPVs is the position of the body and the different leg muscles that come into play to propel the bike [this I can verify from getting on the recumbent for the first time again in three years recently!].
It wouldn't surprise me in the slighest to be disappointed by the output a powerful TDF rider might get out of a HPV over at BM. What they could do if they really out their mind to it? Well, that would be interesting. But to do that, they'd have to put in a lot of training, which would obviously conflict with their existing discipline. And then, you're name might as well be Sam Whittingham.