Years ago, Strava unilaterally disabled the flyby feature on all profiles. They did this without any kind of notice so most people figured the feature was removed completely. Only those who dug around could find that it was a toggle setting in the privacy settings that had to be manually enabled for each person. Only a small number of people figured this out and re-enabled it on their profiles. This action by Strava essentially destroyed the very fun and useful tool.
Flyby is used by many after rides and events to relive how the ride/event unfolded. See where I got away from the group. See where others were faster or slower. See how close I was to catching that guy ahead of me or how close the guy behind me was at some point in the race.
This feature should be re-enabled on all "public" profiles. People with profiles set to private could have it remain disabled unless they have specifically enabled it. This will help maintain the privacy and address the concerns some had that people would use the feature to "stalk" them after crossing paths out on a ride/run. Strava should publish a notification of this change a week or so prior (possibly multiple notifications to ensure people saw it) so users would have sufficient time to choose for themselves whether to go along with re-enabling the flyby feature or opting to keep it disabled. This leaves the choice in the hands of the user.
This was once a great feature, but was broken when Strava made their change. Please consider reversing that decision. By implementing sufficient notice and only applying it to profiles that are already "public", it will maintain the privacy of those who have concerns and allow people the opportunity to disable it if they so choose.