My own explanation doesn't work for me either now.
I've pretty much conceded in prior posts that there are poorly-founded plot elements which I don't have much trouble handwaving away. The one that I stubbornly wanted to resolve was Darkseid being seemingly too absent-minded to remember how to get back to Earth. But if resolving that with the Boom Tube explanation just opens up other cans of worms, then there's no point dwelling on it.
We can just go with the point of view that Khev explained a little earlier: In the vastness of space, and from potentially a whole separate universe, Earth was as lost to Darkseid as a needle in a haystack.
There's too much fun to be had over four hours to worry about every silly plot point having airtight logic.