Hmm? That seems odd to me. As a Southerner myself, I know more people who drink their coffee black, straight (No milk, no sweeteners) than I do people who put stuff in their coffee.

I've lived in the U.S. my whole life and I've never gotten automatically-sweet coffee unless I order something like a flavored coffee drink.

Really? I drink my coffee black both iced and hot. Never had anyone question it.

Southerner here, no cafe or coffee shop would think twice about a black coffee, or cream only with no sugar.

Diners generally only pour the coffee, you fix it up however you want.

Individuals may give you grief of they're making you coffee in their home, but that's particular to them.

You're right about NY, though. Very different vibe.

I don't know where in the South you were. But in the rest of the US, when you order coffee you will usually be asked "cream or sugar" in the event you don't want it black (no cream no sugar), which is the default.