I suspect that Snap is merely capitalizing on traditional advertising metrics (engagement, CTR) which don't translate over on their app, and the advertisers just haven't caught on yet. People play with filters because they're funny/amusing, but those impressions don't convert into purchases in the same way other types of ads would.
Earlier last year Snapchat temporarily featured X-Men filters exclusively ahead of the movie release - I interacted with those for the novelty (and mainly because they disabled all the other filters so there were no other options) but I did not see the movie.
Again, I'm not sure if they follow something similar to a CPC model or what, but I bet it's expensive. If the advertisers decide it's ineffective their newfound revenue growth certainly won't be sustainable.