BecUse he's not doing anything to bridge the gap between the window of prospects, somewhere like 4-6 years away, to the window of guys like Bergeron, Chara, Krejci, Rask, etc. How do you tie these two groups together? That's the question. That's the issue.
Well, the thing is, he still has time to do that. It can happen in the offseason, or at next year's deadline, or the next offseason. It doesn't have to be now, or we're screwed in 4-5 years.
And sitting on his hands... he had to replenish a prospect pool. There was a large talent gap there before 2014-16 drafts. Previous trade talks have rumored to revolve around Pasta, Carlo, McAvoy because those are the guys that have shown high end talent (all non-starters) while the other guys are more like B to B+ prospects that need more time to mature, to be centerpieces to trades.
PLUS, there is the expansion draft in the offseason. I feel the biggest need for the need is Top 4 D, preferably a 1-2 LHD that can take over for Chara, but if they make a trade now, then CMiller will be exposed in the draft, or otherwise needs to be included in the trade. For the D, it will be best to wait until either right before the expansion draft, when they could take advantage of a team needing to move a D they can't protect (like ANA) or right after when they could move from a position of strength will Carlo and CMiller still on the roster.
Landeskog could also be had in the offseason, with expansion over and know what salary has been selected from the team (McQuaid or Beleskey or KMiller or not). Colorado is in no hurry, not like the Bruins prospects would be helpful for them now as opposed to then. For example, it could be someone else too. Point still stands, with the expansion draft, making a hockey trade is even more difficult than ever.
Also, to a point you made a few pages back, they don't need to wait until ALL the next wave of prospects are in their prime to be contenders. Some will need to hit their peek to be contenders, that's a given, but some could be 3rd liners or 2nd pairs, with the old core (March, Berg, Krug) at the top and Pasta, Carlo, McAvoy and Vatrano as part of the new core in their prime, JFK or Lauzon or Bjork or Debrusk or Gabrielle or Senyshyn filling in quality minutes lower down the roster. PLUS, there are several more drafts and free agency periods between now and then. And some of those B guys will step up and be more valuable in trades (some will flame out or hit a Chris Bourque wall).
Way too long story short, they don't need to make big moves NOW for that 3-4 years in the future team, and it is very difficult to manage trades anyways with Vegas. A rental might not be the worst idea. Maybe a Vrbata can bump Hayes down or out and that would be enough.