Rebuilding is done in two scenarios. One, you try, but just suck. Two, your best players choose to leave. Tavares left, which would've been the rebuilding time, but as has been said, Lamoriello is not a rebuilder. He got lucky that Stevens was awarded as compensation for the Blues signing Shanahan. Had it been Brind'Amour and Joseph instead, there's probably no Cup, let alone 3, but the Devils would've just kept on keeping on.
However, most GMs are not rebuilders. Even the rebuilders aren't rebuilders. At best, they're reluctant rebuilders. There's no guarantee it works. No guarantee you have a better team 7 years from now than you have today. Or that you have the job in 7 years.
The Islanders have already invested too much in their current group to do any real bottom up rebuild. They're years and years away from that being a legit option.
Also, look at the last decade of the drafts. There are like 9/10 franchise guys since like 2014. Leon, McDavid, Eichel, Mathews, Tkachuck (if he was taken where he was rated), Makar, Heiskenan, Pettersson, J. Hughes, Bedard. Some very good players in that mix like Marner, Svech, Dahlin.
On average it is 1 franchise type player and 1 very good player in the top 5. So, if you are not lucky enough with the lottery to land one of those 2 players, it's a very long rebuild.
I mean, Anaheim has gotten in 5 drafts of missing the PO, Zegras, Drysdale, MacTavish, Mintyukov, Carlsson. Who is the sure fire franchise guy of this group moving forward? And that is with a worst, 2nd worst, and 5th worst finish in the overall standings. Plus what they get as a 3rd worst finisher this draft.