Wonder Woman mentions in the history lesson in Zack Snyder's Justice League cut that, when Darkseid/Uxas was defeated, the 3 motherboxes were left on earth and also the anti-life equation was carved here. When Steppenwolf mentions a motherbox to DeSaad, why did DeSaad not remember that this is the same planet where anti-life equation is carved? Even if we assume that earth was forgotten after the defeat for a long time, they should have remembered about anti-life equation when motherboxes were mentioned. Please explain if this is a plothole or there is an explanation from comics.
If there are other Mother Boxes, either to be discovered in the wild, so-to-speak, or lost by other Apokoliptian conquerors, then it need not be the case that the discovery of any Mother Box means the discovery of the Mother Boxes from the Defiance- Darkseid's one and only loss.
We can deduce that Apokoliptians have not had Mother Boxes from the beginning and did not create them using the Fermi Paradox. If Mother Boxes are a billion years old... that is practically 1/10th of the lifespan of the entire universe! If Mother Boxes had been possessed from the beginning and used to terraform from the beginning... there's no way we're talking about only 100,000 some-odd worlds! In practical terms, the entire universe should be swarming with its conquerors at that time scale. This is the essence of the Fermi Paradox... Earth's been around for 1/3 of the whole universe so "where is everybody?" why haven't aliens spread here yet?
This means that Boxes are something Apokoliptians need to discover or recover from a lost precursor civilization that predates them. That means they run into them from time to time. They aren't all evidence of the Defiance. Additionally, while Darkseid and Steppenwolf speak of their victory records, remember that they're top dog and the right-hand-who-was conquerors... the best-of-the-best Apokoliptian royalty. Doubtless there are other conquerors trying to move up the ranks, earn their spot, take their shot (Steppenwolf is literally in exile for participating in exactly such a game of thrones!)... and some of them have failed, fallen, or lost their Mother Boxes to other worlds.
This is partly the relevance of the "No protectors" line because if your win record is 100% why would you care about protectors? It's because either you're ducking them or because others of your ilk have lost to said protectors.
As for Darkseid "forgetting"... we only have Diana's hearsay on that. There is a much more plausible reason the location was lost.
Zack Snyder has explained via Twitter in answer to the same question.
"He almost died when he returned to Apokalips. He was in a fight for power and much time passed before he was in a position of power again, and by then all who had been with him had been slayed."
Basically he was wounded so badly he could not recall where Earth was and the had to search over 100,000 worlds before it was found again