The Space Invaders were, as are all highly developed sentient creatures, humbled by their mistake and learned from it. The unwarranted presumption was corrected in order to benefit all involved, and allow peaceful coexistence to prevail.
Humans were observed to be ravenous consumers of edibles, but were also narrowly selective in their choices, and the aliens hastened to satisfy these needs. The goal was not to decimate the population, of course, but to keep it in good order and health for entertainment purposes.
Immediately the invaders disassembled the Mother Ship. It was sliced, chopped, and ground into prime cuts and patties which proved delicious to humans, and sold the resulting pieces for what is called 'cash'. The enterprise was wildly successful, proving that the laws of supply and demand were always applicable and lucrative.
With newfound assets called 'profit', the aliens embarked on acquiring their heart's desire, which included Dreamworks, USA Network, and Skywalker Ranch, financing cinematic adventures where slug-like eight-legged fuscia slime creatures were always the romantic heroes.