The Bruins don't rebuild because it's not a winning formula. Ask Buffalo how permarebuild is going for them. As for Jersey, I've been hearing they're on the rise for at least 5 years now. Nothing good has come of it.
Yes choose the one failed experiment to try and prove a point while completely ignoring the ones that were successful. The point of a rebuild is scout, draft, and develop your core to move forward with. Then you fill in the holes with free agent signings, or trades using the expendable assets you've acquired over the course of your rebuild. The last 5 different Cup winner's cores were largely built through the draft, so idk how tf you can confidently say it's not a winning formula.
Colorado: MacKinnon, Rantanen, Landeskog, Makar, Newhook, Byram
Tampa: Stamkos, Kucherov, Point, Killorn, Hedman, Palat, Vasilevsky, Colton, Foote, CIrelli
St Louis: Tarasenko, Perron (returned), Pietrangelo, Schwartz, Dunn, Thomas, Parayko, Steen, Barbashev, Binnington.
Washington: Ovechkin, Kuznetsov, Backstrom, Carlson, Wilson, Orlov, Vrana, Burakovsky, Holtby, Grubauer
Pittsburgh: Crosby, Malkin, Letang, Guentzel, Fleury, Murray, J Staal and Orpik (2009).
But hey, I guess you would know about Boston more than I do. Have fun continuing to do this little purgatory thing you got going where you don't fail but yet are never seen as a true contender. Your one single championship in the last 30 years really appreciates it. Can't wait to see what you think when your core of Marchand, Bergeron, Krejci, and Pastrnak are all gone in the next couple of years and you try to build a team through your non-existant prospect pool.