On Meetup and Strava Cycling Events
Meetup and Strava are two sites filling specific niches. Meetup is a dinosaur of the web. It dates back to 2005 when the web was still looking for a way to be sustainable, and thus, more fun. Meetup was good for people in big US cities, London and other metropolitain cities. If you lived in Bumbleduck nowhere it was not. (Intentional spelling)
Strava in contrast is a young company. It was created in 2009 and became popular among the cycling community for a while, before eventually including running, hiking and then climbing and many other sports. The point of Strava is that it is a social network for sporty people. Meetup is a social network for sedentary, as well as sporty meetups.