Why did the leafs trade up to get cooley ?

Please understand that getting Nylander with no guarantee of a contract just does not have tremendous value and is high risk for the Devils rather than just picking 2nd...

Pens decline, we aren’t going to sacrifice losing a key bottom 6 LW to build up our RW depth. Although, a 4th for Kase straight up would get you the deal.

Bruins and leaf aren’t making any trades.
Devils definitely decline. So do pens.

Why would Jersey trade their 1st pick for a player with no contract?

No guarantees anywhere. You could draft a bust at number 2. Nylander is a proven 80 point player. Risks on both sides.

Pens pass, we're already all set with concussions, no need to add extra.

I posted it in a different thread where someone had the Devils trading 2OA so thankfully I can c/p it here. This is the decade of #2 picks from 2009-2018 (skipping the last 3 years because those guys haven't had as much time to build up a resume):

2009: Victor Hedman (Norris Trophy & Conn Smythe Trophy winner)
2010: Tyler Seguin (305 goals in 825 GP - pretty good!)
2011: Gabriel Landeskog (248 goals in 738 GP, Calder Trophy, captain of a Cup Final team)
2012: Ryan Murray (even in a year when everyone missed the top 4 guys, still has 432 GP in his career)
2013: Sasha Barkov (Byng Trophy, Selke Trophy, 220 goals in 596 GP)
2014: Sam Reinhart (167 goals in 532 GP, finally a PPG player in Florida)
2015: Jack Eichel (153-227-380 in 409 GP, consensus #1 in any year w/o McDavid)
2016: Patrik Laine (176 goals in 407 GP, PPG this year with CBJ)
2017: Nolan Patrick (ugh - 77 points in 222 GP, ruined by head injuries, shoulda been Makar or Pettersson)
2018: Andrei Svechnikov (89-120-209 in 283 GP, loves scoring cool goals)

Out of 10 dudes, there are 8 there who I would argue are on par/better than Willie Nylander (especially considering you're going to be paying him 2x$6.9M and getting at least the first 3 years at $925K from #2OA.) Even in mediocre draft years, the guys picked up the top 3/4 picks tend to be impact players, and I don't think it makes sense for Jersey to trade that pick unless they're getting absolutely blown away by the offer. And Severson/Zacha/2OA for Nylander/Sandin/Niemela just isn't enough, to me.

Absolutely, a player could be a bust, but I'd rather have the younger asset than a player that could walk away in two years. Your plan only works to the advantage of the Leafs that need cap room and to win now, the Devils are looking beyond two years.