It's not clear if The Bet wasn't made just before the making of current world.
Also, It seems the monuments are to honor worlds and souls devoured by the Snarl, so no souls for Hel.
And now I start to think if The Bet and Durkon's prophecy aren't. It made me remember American Gods, those who have read it will know why...Spoiler: Possible Spoiler about American Gods, by Neil Gailmanpart of a big Odin&Loki Con Act to try to solve the Snarl Problem once and for all