I probably don't know as many hunters offline as some, I quickly counted maybe 50ish, but I only know one other that regularly saddles and he's a tree guy that migrated from that world with his work gear.
The vast majority of guys and gals are convenience hunters, embark on hunting journeys only out the back door of camp or home, use fixed stands or blinds and most immediately balk at the suggestion of any degree of mobility. I think the logistics of hunting alone is a bit of a pain in the rear for a lot of people, and what we do seems way insurmountably complicated to those folks.
That leaves around a half dozen I know that regularly go mobile, most of those in traditional treestand configurations but I believe all of that group is at least aware of saddles, most are just too set in their ways to change.
Not a statistically relevant sample size, but not tiny either. I'm in my 30's so I have a pretty good spread of ages I am acquainted with.
The internet can make it seem like our clan is larger than it is, especially with a lot of the bigger influencers lately adopting and espousing public land, mobile hunting, and saddles, but when you get in the general population we're still rare birds. A lot less rare than 5 years back, but still rare.
As for figures, I can't imagine much more than 2-3% of whitetail bowhunters (inc Xbows) are in saddles. That may even be high. I've seen ATA estimate active bowhunters at around 5 million. Cut out maybe 25% of those are western ground-type hunters, that are very marginally in the saddle/treestand market to begin with, I'm calculating ballpark 100,000-150,000. That's a tenuous calculation but it's one step beyond a wild guess.
The market is not very large and I believe we are living in the peak saddle epoch presently. Max gear choices, now is the time to try and buy. In the next five years I expect there to be significant contraction in the market.