It’s an Anglo-American ‘Italian’ thing, not an Italian one. No Italian chef with any self-respect would send out food and expect his waiters to season it.
No way can it be to prevent theft. Rubbish. If I wanted to steal from a restaurant, I’d eat the meal then do a runner. I wouldn’t steal a bloody peppermill.
Noooo, if you REALLY want to insult them, ask for ketchup with your steak! 
Olive Garden was mentioned above.
The one I have been to a few times, does the ‘pepper mill thing’ with grated cheese.
I’ve always asked for my own shaker of cheese because I like a little on my salad, a lot in my soup, and maybe none on my entree. I can’t see the waiter returning as each portion is served. That’s just dumb.
From reading some newspaper accounts, I’d say that the idea of the two foot or taller pepper grinder in fancy restaurants started in the very upper eschelon of the group in the 1950’s. The custom, as I read it, was considered to have come from Europe, but probably not much earlier than this time frame. It certainly didn’t filter down to more average restaurants until the late 1960’s/early 1970’s.
And the article I was reading about a very exclusive one in 1958 was talking about how the clientele were not above stealing the shakers.