The story is that the tower/ship has just arrived. That is the situation every time the guests enter it. Peter Pan hasn't been flying guests to Neverland for 50 years, it happens the one night you get on the ride.
So, the tower has just arrived and the Terran visitors are the first to see what the heck The Collector is up to. Before they can call the police or the Avengers, Rocket enlists their help for the Guardians to escape.
Why hasn't Earth authorities already investigated an alien vessel? I don't know. Why aren't the media crowding Dumbo to take pictures of a flying elephant?
Why haven't the Avenger investigated? Even if the park's version of the Marvel multiverse was the same as the MCU (which it is not), at the time it arrived, only Thor would have known anything about The Collector. They're either busy with the events of their own attraction, or, the standard comic book reason is: They're off world. The new sign has The Collector saying "he's heard of the Avenger" and "he welcomes them." There is no previous history here in this story line.
But maybe one day,
@lazyboy97o, your line of Disney's approval of slavery will finally catch on... somehow. Keep at it. We're rooting for you!