It was hard to say if Malekith, who had survived since Bor's era, had any backup plans.
Asgard could only do its best to take precautions; everything else depended on luck.
Luke could confirm that Malekith really was dead.
However, he couldn't guarantee that this first-rate boss wouldn't be resurrected or cloned or something.
In any case, how Asgard wanted to handle this had nothing to do with Earth, and wasn't something he needed to concern himself with.
Taking the Bifrost was a wonderful thing.
It was even more so for someone like Luke, who was very knowledgeable, had superpowers, and had a strong physique.
He could finally experience some of the things he had read in the information obtained from Thor, and could even see more secrets.
The Bifrost's teleportation wasn't fixed, nor was it instantaneous.
A person could even move to a certain extent inside, but if they used too much force, they would fall out.