That’s a curious thing to me since the Orthodox always refer to a priest as Fr. first-name. Of course, Orthodox parishes are smaller by design so there is more of a personal connection to individual clergy and it’s not uncommon for a priest to serve at the same parish for 40+ years.
I didn’t know that about the Orthodox. I’ll grant that habit and customary usage have a lot to do with these things. But common modern American usage is honorific+surname or just first name. And Roman Catholic usage has always been Fr.+surname.