It's amazing how you didn't even read the thing you quoted evidently:

if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defence recognized by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.

What do you think" exercise of the right of individual or collective self-defence" and "such action as it deems necessary, including the use of armed force" means exactly?

It means that individual countries get to decide the level of support they provide ranging from nothing to getting involved militarily.

And no, despite Russian fanboy insistance, the US isn’t low on ammo. From the Secretary of the Army’s testimony to congress:

US aims to go from making 14,000 155mm shells each month to 20,000 by the spring and 40,000 by 2025. This is the amount of shells Russia uses per day in Ukraine.

And of course, the problem for US is the state of its industry you can't just create factories, supply chains, and trained workers out of thin air the way you print money.

It's pretty clear that people who believed all the bullshit before the war have learned absolutely nothing throughout the war.