I'm not sure this is an "exploitative relationship", unless you also define your relationship with a supermarket chain or netflix to be "exploitative". You give money for a service. Said service tries to extract money as efficiently as possible.

It's a capitalistic relationship, certainly. But it's very different. reddit volunteers provide their efforts to improve reddit's brand, for free, generally just for personal gratification (from people who will turn on you and drive you to suicide the moment you make the wrong move). Thos efforts are exploited by reddit, rather than rewarded.