For new variants travel should be shut down immediately, and then study to see when we should reopen the travel.
But, "new variants" come up all the time. Constantly, because anything with the slightest genetic difference is, technically speaking, a new variant. Like, statistically, every person who gets covid probably produces a new variant. If you shut down travel for every new variant, then travel is shut down permanently. If you trigger on every single new variant, you will be paralyzed.
So, we need some other threshold for a new variant that we need to be concerned about. But, evaluating the threat presented is complicated, and requires some judgement by experts... which is what you have now.
Edit to add: And oh, look, after consideration, the US is stopping travel to some African nations of this. Almost like the system works as intended!
And, interestingly, they are calling this one Omicron. If they've been naming sequentially, then, and the one we've generally hearing about has been Delta, that means there have been ten other variants named since Delta, but that turned out to not be a big deal.