It's no secret that Kent Hughes is actively trying to trade Jake Allen, but he won't give him away. In his eyes, the goaltender has value, and it's out of the question to trade him at a discount.
We know that the Maple Leafs offered a 6th-round pick to the Canadiens, and that's pretty much the best concrete offer that has been confirmed. It doesn't seem sufficient, but there's a detail that wasn't known.
So, without salary retention, Hughes might have accepted a 6th-round pick, but with retention, he wants nothing to do with it.