A lot of people come for the atmosphere and other festivities. I'm sure the actual number of people visiting town for the game is closer to 200k than it is to 50k.
For some people (not fucking pats fans though), this is a once in a lifetime chance to see THEIR team play in the biggest game . So yeah, people travel, migrate. For some people it feels like a religious journey. All of your kin are migrating across country for this one event... Just being in the city is cool, you will be seeing rams / patriots jerseys all over Atlanta for the whole week!