The footprints I’ve seen are natural impressions in the rocks. You’re right about the similarities between Buddha relics and slivers of the cross, etc. Maybe some people need physical proof for their beliefs.
I don’t think necessarily physical proof. It’s sort of like autographs. It’s just really exciting to have something that was part of someone you admire. That’s why Catholic relics are popular from first class body pieces to 2nd class, frequently used objects, to 3rd class, came in contact with, objects. A rosary of Pope Pius XII would be a big deal not for any “belief” in him but as a reminder.
I put objects in the hallway that remind me of special moments I’ve shared with my husband, and things that make me stop for an instant and remember why I admire them, not just for their art, but for their backstory.