Mostly the other NHL teams for being dumb.
Look at most of their top players:
- Marchessault was unprotected by Florida so they could protect Alex Petrovic who is now been healthy scratched a few times. Marchessault is now Vegas' leading scorer
- Smith was also given away by Florida for literally nothing even though they had no obligation to do so whatsoever. Smith is now a big part of Vegas' top 6.
- St. Louis protected Ryan Reaves over Perron. Perron's on pace for 20 goals and 70 points this season and the Blues don't even have Reaves anymore.
- Boston protected Kevan Miller over Colin Miller and now Colin Miller is a top pairing Dman on Vegas with Kevan toiling away on Boston's bottom pair.
- Washington left Nat Schmidt unprotected instead someone like Tom Wilson who's pretty much the definition of a plug forward in the NHL. Nate Schmidt is basically Vegas' number one dman right now.
- LA decided to protect someone like Derek Forbort over Brayden McNabb who has been a stalwart of their defense corps.
All of those players are on Vegas right now as a result of other team's mismanaging their protection slots. As for the others, a good handful of them were given up from other teams who were forced into sacrificing younger talent in favor of NMC's they had given out in the past.
- Columbus could've protected Will Karlsson over Dubinsky if they hadn't given an NMC to Dubinsky who's a pretty average middle six player. Karlsson now has 20 goals and leads Vegas in scoring.
- Minnesota could've kept Erik Haula and Alex Tuch if they didn't shell out all the money to Suter and Parise who both had NMCs. Both of Tuch and Haula are producing well for Vegas.
- The Rangers could've kept Oscar Lindberg if they didn't give Rick Nash or Marc Staal NMCs.
- Ducks gave asay Theodore because they were hamstrung with Bieksa’s terrible contract.
You can continue to go down the list. James Neal and MAF are the only players who I can think of as players who weren't sacrificed as a result of poor management (as far as key players not counting the Leipsics, Bellemares, Sbisa, Merril etc. etc.) the rest were given away for free either by other teams because they didn't think they worth anything or they were hamstrung by past mistakes. You also have to wonder why players like Karlssson, Haula, Miller, Schmidt etc. who are outperforming a lot of players on their former teams who they were playing behind in the lineup at the time, why were they not playing ahead of them on their former teams? Why were they not given a better opportunity?