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.
I had noticed the difference previously and I sort of attributed it a necessity given the greater number of priests in the Roman Catholic Church in addition to the Anglicized names.
Bishops in the Orthodox Church drop their surname completely although they'll show up in print with brackets around them whenever there are multiple Bishops with the same first name (which are taken when they take their monastric vows).