Why do some TikTok slash&free items hit $0 fast while others feel impossible

I have been watching those “slash&free” games on TikTok and noticed something odd. Some items hit $0 with just a few friends tapping the link, while others barely move even after a bunch of people help. It really does not feel random. It feels like the app is quietly changing the “difficulty” based on the product or the user.

My guess is it might be tied to things like margin, inventory, how viral the item is, or maybe even your own behavior on the app. Some products feel like loss leaders to drive sharing, while others seem to need way more cycles before they get close to free. Has anyone here looked at this from a growth or pricing angle, or seen any data or patterns on how this is actually tuned?