Reddit had no monetary cost.

It's much easier to stick to a boycott when it requires a layer of active acceptance and payment to acquiesce.

Reddit is just... there. A query on basically any search engine is going to serve you up reddit links, and clicking one of them costs you nothing.* Since you don't have to commit to the decision there's far less resistance to backsliding.

*Yes, I know, there is a privacy and personal content/traffic cost. We both know that's not what I'm talking about.