Other than authorial fiat and the whole "repurposed stock images" thing? I dunno, they needed a big slab of America, Captain America was busy and Superman never returned their calls?
Seriously, though, there is absolutely no explanation. Page 8 just shows that the Rabbit was asleep...uh...somewhere...and they just kinda found him.
Worse yet, I don't get the whole idea behind him: there are icons all over the place who are miles more recognizable and hallowed than the Rabbit, and the time skip he experiences, if we assume he "fell asleep" in the mid-80s after his last movie was supposed to have taken place, he'd only have been away 20 or so years, which isn't long enough for everybody else to have cheesed off or died or whatever. I talked about this with a friend-the most he'd be shocked by logically would be things like "what happened to Russia?!" and "all the technology's TINY now!"
Here's my bigger question: why is the blurb even suggesting the story is mostly about him when it's actually about Stock Brunette trying to figure out what's up WITH the American Rabbit?