I'm sure Carolina doesn't need DD, and Arizona is strong at centre and don't want Plek at 6m a year. Edmonton could use Emelin's 3m to better use.
Carolina can easily fit 1 year of cap space for a decent 3rd line player to get a better pick at the draft. Plek for 2 years is affordable with phoenix and he'll be good for the young players. They also get a very good prospect in Scherbak and a future starter in Fucale AND a 2nd round pick which more than makes up for Trading the 9th pick for their 7th in this deep, deep draft awaiting.
The worst part is that DD isn't even all that bad. Its just that MTL desperately needs bigger players. If DD is given some big/strong wingers to play with, he still has some value. But alas in a NHL where every penny counts and most teams would rather spend elsewhere DD is a hard sell. His line with Flash and Weise was the main reason the Habs had the record start they did.
The Pleks trade funny enough almost makes more sense without Plekanec in it. When you rationalize it a bit, MTL is pretty much giving up four (former and current) 1st rounders for Duclair and the 7OA. Scherbak 26th. Fucale 36th, 2016 1st (9th), 2016 2nd (39th). All "pretty much" 1st rounders. I would at the very least consider it if i were Arizona. Regarding Plekanec himself, poor guy will never get much recognition. 50-60 pt center who is widely considered among the top (non-Selke finalist) defensive centers in the game. People are scared away by the 6 Mil he just signed the most but when considering its only for 2 years and signing a UFA center of that calibre will cost you a minimum of 5-6M for at least 4-5 years, your getting a top end 2nd line center at current market value for half the term it would cost you on the free agent market. Oh well fine, looks like MTL is "stuck" with Pleky but in all honesty, thats one of the good problems to have. He is by no means anywhere close to the equivalent of a Girardi or Staal in NY if some people think that.....
The Emelin trade is probably the hardest sell. The guy is simply not good enough. The big checks make him flashy and possibly worth taking a gamble on but most GM's know by this point his foot speed and decision making is just good enough to command anything more than a 1.5-2M/year contract. Anything higher and a better option is automatically available.
I don't know why anyone would want to trade Flynn. The guy is the definition of 13th forward and performs it to a "tee" He has so little negative impact on the team that there's no point in trading him. His PK skills are highly underrated. He and Mitchell were amazing early on in the year until they both got injured. if for whatever reason you don't like him anymore, bury him in the minors for full cap relief.
Why would you trade Desharnais and a 3 to move down two rounds in the draft?
The idea is that if you take DD off our hands, we'll improve your draft pick. Gives MTL more cap space and gives the other team decent player and a better draft position.