In reality it does often offer perks (seeing creative work before release, exclusive behind the scenes stuff, etc.) so I think you can see that as a purchase, no?
Belonging to a church often has perks, yet we don't consider offerings purchases. I do think some Patreons are setup closer to a shops, but not all.
We probably should tax churches, since many churches require tithing and offer a pretty outstanding benefit for membership. It's hardly a donation when you're donating to an establishment central to your everyday life.
It's basically a social club that gets a pass on taxes because they believe in magic.