The real reason it hasn't happened is because the vast majority of the USA has "good enough" Internet service.

As long as Netflix works, and email sends, people don't care too much.

WE love symmetric gigabits and spend all day downloading and uploading Linux ISOs, but the average American doesn't.

Even in places, like where I am, where fiber has appeared, it hasn't really changed how people use the Internet.

Or to put it another way, there's not yet been a killer app for symmetric gigabit connections, so there's not a terrible amount of demand.