So aliens have visited your planet and left, what's a civilized world to do next?
How about: Do the stupidest things imaginable because it's the only course of action that can be agreed on, even if it doesn't do much of anything to fix the "alien problem?"
That's pretty much the world Penn is born into in Sing Down the Stars. A quarter century after alien visitors appeared in the sky, then left, the world is still debating whether or not those visitors were ever actually there in the first place. And since bureaucracy can be counted on to take the strangest courses of action, that uncertainty has manifested in odd ways around the world.
Since the aliens came to the modern world, twisted logic dictates that they weren't - and aren't - interested in cultural landscapes of less modern times. With this in mind, entire cities have rebuilt their structure to mimic that of earlier days. Some went Victorian, others hopped back to the 1950's, and some simply froze in place, refusing to allow any public signs of progress.
Major cities have moved their technology underground - both figuratively and literally. Nighttime means radio silence, television silence, computer silence, and total blackout as the official policy for avoiding mentions of alien invasion becomes to pretend it never happened. Earth simply decides they won't attract attention.
With this in mind, it's easy to imagine that special events like The Show, with its permits for lights and lasers would be a huge draw for the curious. Kids born into the post-alien world don't get many chances to see cutting-edge technology on public display, so crowds flock to the circus grounds like naughty children who think they're getting away with mischief.
This isn't a brave new world. It's a timid, and anachronistic one.