Why not then blow up the Norway to Poland gas pipeline itself?
People ignore acts of war all the time to keep the peace where nuclear arms are involved.
NS1 and NS2 aren't shipping any gas, and notionally are "Russian": dramatic but no change in the status quo.
Blowing a pipeline between two NATO members which is shipping gas and imperils their population is very different: NATO can't ignore that.
Attacking Norway-Poland line at this point would be a very obvious and very direct attack on NATO.
Some of the NS attacks were on NATO territory. Denmark could invoke Article 5 were it found to be Russia. If "NATO" were in the equation, the saboteurs would have stayed in Swedish and Finnish waters, and even then it's iffy.