I just want to second @coboat 's comment. My first time using couchsurfing I surfed for 4 months, and I don’t think I ever attended an event or really knew anything about them. It was just after I returned home and was back on the website that I figured it out.
Make events very prevalent. Nudge new couch surfers a week after their first time surfing with a link to attend an event near them. As coboat said, making active communities is the first priority, but once that’s in place, give the new members a nudge to join in. Event organizers should be able to invite incoming travelers to events like ambassadors could (maybe not full bore, with some kind of brake for organizers who spam).
If they stay connected with this community, they’ll see people bringing their surfers to events, it’s an easy step from there to get that surfer hosting him or herself. And while there may be plenty of dropoff this way, I’m strongly against any sort of incentive that will turn hosting and surfing into a transaction. Because that’s what I just quit.