I don't know, but there are different segments that add up. And TikTok, YouTube, and Facebook make grey seem like no big deal. Type "reta vial" into Google and you get Google legitimizing grey through sponsored product listings. Facebook has a ton of ads for overpriced single vials.
As mentioned before, the med spa people are a huge percentage. And it's true that many/most people don't even know they are going grey by getting some things from a med spa.
You've got gym and steroid users using peptides, especially reta, HGH, HCG, and BPC-157. And some guys start doing TRT legally but then want higher dosing. The whole grey market really started with steroid users, is my understanding. And some Chinese vendors make more selling steroids than peptides.
Then you've got the beauty crowd that doesn't want to donate money to med spas, even doing Botox at home thanks to YouTube videos and shipments from Korea. Korea is the best source for glutathione, btw.