But by the Alter Rebbe’s time (and how much more so today) the fire and brimstone effect wore off, gehennom burnt down, and it wasn’t inspiring people anymore.
So they were thinking of making gehennom scarier, but the tzaddikim said that its not gonna help for long. Better idea to bring out the beauty of Torah and mitzvos, and how we have the best life possible, refurbish gan Eden.