Why the Space Marauders of Ganymede were chosen to help prevent human extinction on earth

 The problem the Galaxy faced was one of the somewhat suicidal behavior of the populations of earth. It isn't that ALL people individually are suicidal but as a group we are as humans here on earth tend to overpopulate ourselves to extinction. 

How does one put this?

Maybe the best way is to just be direct about this. What other species allows it's members on earth to keep reproducing until all of them die from overpopulation?

The only known species to do this is human beings here on earth. You might have maybe some bacteria or viruses like Covid that might act like this but basically no species just keeps reproducing like humans do until they all die from overpopulation. 

This is a given (at least here on earth).

So, because the Galaxy operates Galactic Park Earth which is one of the many Galactic Parks in the Galaxy (the whole planet for millions of years) (Possibly longer than 100 million years because permission had to be obtained for the survivors of the Planet Maldek and Mars in from the Galaxy for the survivors 65 million years ago when Maldek nuked out of existence into the Asteroid Belt and some of the pieces of Maldek came to Mars and knocked a lot of the atmosphere and water off of Mars which left it in it's present state. So, the residents of Mars had a choice.

1. Leave the solar system if they were rich enough to return to where humanoids came from. OR

2. Get permission from the galaxy to live on earth which at that time had T-Rex and other dinosaurs just ready to eat any humans who came there.

So, what appears to have happened is one of the asteroids from the explosions  on Maldek hit the Yucatan peninsula here on earth which created a multi- year nuclear winter kind of event which froze to death or starved to death all the larger dinosaurs too big to hide in caves or to migrate into the oceans as a means of long term survival.

After a couple of years of dead T-Rex's and other large dinosaurs Earth became a lot safer for survivors from Maldek and Mars to come here to earth.

So, they did also about 65 million years ago.

Ever since then they came and stayed or died off in ice ages or had relatives come pick them up and take them to other planets ever since.

So, we are just the latest version of the human race that didn't die off or leave during the last 65 million years time.