The issue here is that the state with the most motive (Ukraine) is one that most are agreed did not have the opportunity to actually conduct the attack. Nobody else has a strong motive. The US had already achieved what it could have hoped to achieve months before the pipeline explosion. Russia's plausible motive assumes a certain amount of strategic insanity mixed with thuggery. Everybody else's motive more or less rests on making a political statement that they haven't been making in public.