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.
Yes, all of which can be purely personal and not shared beyond the device.
For me it's both. I compare my runs on routes and segments going back years. The social part is nice to share info about trail conditions and see when my friends hit a big effort or PR.