There’s an argument in Atlanta that mass transit hasn’t expanded more outwards because it tends to bring in more problems in terms of people. I think people are starting to change on this, but the cost would now be massive,
Too bad they screwed this up when they built the International Terminal, which is connected with a bus on surface streets that gets stuck in traffic and at lights. If you're flying an airline with a presence in the domestic terminal, you can use the internal transit system to get to the International Terminal but otherwise you're stuck switching from the train to the bus or vice versa. It's an annoying bit of extra friction that shouldn't exist.