The popularity of Goshuin stamps and visits to spiritual spots like shrines and temples is not a show of faith, experts say, but instead suggests people feel an affinity for the traditions without a need to be deeply involved. Some compare the stamp collecting to a blessed version of baseball cards.
I mean you dont have to be religious to appreciate the stuff religion makes. Giant temples, cathedrals, towers , statues and such.
Shrines just capitalize on the japanese tendancy to “collect” stuff.