That's way too much for the Leafs to give for two middling Seattle players. Plus it takes on more unnecessary long term cap in Larsson. Besides trading away two NHL Dmen and only getting one in return leaves the Leafs weaker on defence.
Nothing in the Ritchie trade for Arizona to accept.

Don’t see why vegas would do this

This is certainly a weaker team. Holl is as good as Larsson and likely better. The guy does nothing. He never has the puck, can't really pass, doesn't skate with the puck and blocks a pile of shots because he never has the puck and gives up major shots against. Larsson isn't good and hasn't been good, ever.