This is stated in the article.

The theory is that explosives on NS1 were detonated because the failure of NS2 would have triggered an inspection of NS1 that would have revealed the previously planted explosives.

Not mentioned in article, it also explains why the NS1 was blown up 17 hours later than NS2. Would expect coordinated attack to occur simultaneously.

Also, it explains why NS2 leak was distance from NS1. If coordinated attack, would expect one ship to lay explosives on both pipelines close together.

How do you trigger these kinds of things? I don't think radio works at depth. So you need to actually get close enough for a sonar ping or whatever? Hmmm, 80km in 17hrs...

Well, because as he said, they so far confirm to have found explosive residue at one site, and not the other. And, as stated, there was suspicious activity of a ship directly over the site for a week prior to the attack, where explosive residues have been confirmed, and not over the other site.

Because the theory is straw-clutching to discredit Hersh. These kind of pipelines have extremely rigorous testing regimes. The probability that a weld defect caused failure in a non-operational pipeline is tiny.

One of my dad's close friends when he was a companion (compagnons du devoir, idk if it exists in the US) worked on submarine welds. He would agree with you (he just retired because army have early pension)

A second welded for EDF on thermic generators, including nuclear. He would have agreed with you, even when he was detached to China. Until 2010. Now he rants about quality control not doing their jobs, 28 years old managers who never welded once in their life who can't bother showing up on the site, and the resp ignoring his warnings for years. I'd say the probability is at least small, definitely not tiny.