Fwiw, from the people I know using Strava, it's less about the sharing/reading other's efforts aspect that makes them use it, and more because of the analysis, dashboards and stuff like that.

Perhaps not, However Gamification of fitness is huge motivation for many people to keep exercising and maintaining the rhythm which in fitness is quite important.

Such social sharing + gamification systems are no different than Github contribution streak or StackOverflow awards for streaks etc. Those streak award only benefited the platform, while awarding us fake points and badges, the fitness streak rewards and social sharing benefits the users health so arguably has a stronger case for being gamified.

We can argue all day that people should want to do fitness to be healthy, not on how they look or other people see them or their fitness, but reality is that the social component of fitness is a big part for many people be it at the gym or in an app.

No but every damn thing seems to be that way by default, so we are expecting everybody to opt out rather than opt in most of the time