For me, there are a few that were just past their use-by date in that they hadn't been used in a while (so were somewhat safely forgotten about), and were heavily tied to a specific era. So I was surprised they were brought back.
KGBeast is the biggest. He wasn't that big a deal the first time (to me, anyway), given the number of rogues Batman has. His origin meant that he had a limited timespan left as a character as time's passage would make it unworkable eventually.
Captain Nazi is both stranger and more understandable, in some ways. So over-the-top, and so meant to be. I haven't actually read the story, but it seems timeslide would eventually push the decedent down a generation (and kill off his brother), there, too, necessitating a reworking.
But maybe they just didn't care about the longevity of particular backstories. Maybe I'm wrong, and people were begging for them be back. I mean, Captain Nazi was part of Freddy's hero origin.