They're easier for people with disabilities to sit at without being in the walkway for waiters/waitresses, especially if they're in a wheelchair
I'm not sure if your question was rhetorical or not but I answered anyways
semi rhetorical. mostly an attempt at humor. and that still only explains why they'd have one or two tables. the steak and shake we went to the other day had booths and tables and they sat us as a booth clearly designed for wheelchairs... one side only long enough for one person with a bit cut out to let a big chair in. so that still does not explain THEIR tables!
Some booths are so small that Im finding it a squeeze to get in and out of them. The larger ones are fine though. You can also see more of whats going on from a table.
I'm not sure if your question was rhetorical or not but I answered anyways