TBH, (and having only seen the theatrical, not the Snyder Cut) the way I headcanoned it was:
-Darkseid and his commanders rampage around conquering planets eons ago.
-Earth repels Steppenwolf and the Mother Boxes get left behind (which are a fairly limited/valuable commodity, but not *irreplaceable*).
-At the same time, Darkseid tangles with Krypton and gets absolutely hammered, withdrawing from the general interstellar neighborhood (including Earth).
-Krypton blows up, but the Mother Boxes continue to detect a Kryptonian presence, so they assume Earth is still a no-go zone and remain hibernating.
-Superman dies, the Mother Boxes no longer detect Kryptonians, broadcast LET'S GOOOOO on all frequencies.
Basically swapping in Krypton as the historical version of New Genesis that kept Darkseid in check for much of the DCAU.