In the South East, they bring you sweetened (usually far too sweetened for my tastes) iced tea. This is amazingly universal.
I live in NC and have been probing the border for years.
For “nicer” restaurants, the universal sweet tea boundary seems to be precisely at the NC/VA border.
I’m pretty certain it’s because it’s so damn hot a humid in the SE US. Sweat tea is a good way to cool down and get some sugar for energy. I’d guess it mostly replaced Switchel, and it’s now pretty much the standard tea drink. If you’re outside, you almost certainly don’t want hot tea.