"It is used by a much broader demographic these days"
Is it? I wonder if that's true.
From a year ago: "Strava has about 8.2 million users, about 1.2 million have posted an activity in the past 24 days, and (perhaps the most closely guarded secret) about 192,000 are premium members."
http://markslavonia.com/sampling-strava/
Now maybe all those figures have doubled, or trebled, in 12 months. It's possible. Even so, it pales in significance compared to say Facebook's 1.5 billion active users in 2015 (not just sign-ups), Or WhatApp's 900 million, Instagram's 400 million, etc.
http://www.statista.com/statistics/272014/global-social-networks-ranked-by-number-of-users/
So it might be fair to say Strava is very 'niche' as a social network service, and probably fair to say most of its users could be considered, if not athletes, at least 'sporty'. :-)
Here are Strava's own stats: no mention of the number of active users, but if you drill into those figures then the user base is either much bigger than the estimate above, or they're just a very active bunch.
http://blog.strava.com/the-big-adventure-2015-animated-11265/