The basic issue US media has with this situation is the same issue they have had a lot in the Trump era: accurately reporting what was done (in this case, the US broke its word on a treaty) would look a lot like a partisan political attack. This would violate the principle of "balance", which by training and ideology they just cannot make themselves do.
US mainstream media during the 20th century essentially grew up during a period of consolidation and monopolistic competition. This meant the consumer had some, but not a lot, of alternatives (usually 2 or 3), so everyone had to play for a general audience and build up loyalty with a "brand". They couldn't really shoot for a niche and survive. If a reader lost trust that what they were reading was going to be an attempt at truth, but instead simple political propaganda, they'd change channels or switch their subscription to the morning paper.
So mainstream US media developed a semi-formal code of political "balance". The idea was that on political issues they would try either not to weigh in at all, or failing that, give the side that the reporting made look bad some chance to respond. In practice this works out to a heavy bias in favor of centrism and normalcy.
Political operatives in the US started learning how to play this media desire for "balance" to their favor back in the 1970's to get themselves softer coverage (particularly the Tobacco companies and arguably the conservative movement).
The difference can be seen quite starkly any time a US ideologue foolishly agrees to be interviewed overseas. (See the relatively tame Frost Nixon interviews, or a lot of folks from the US far right interviewed lately by the BBC). Even relatively savvy US political operatives don't know how to deal with a proper adversarial press interview, because they get so little experience with that in their native country.
This "balanced" reporting works pretty well in normal times for normal stories where normal things are being done and both sides are acting in good faith performing actions that can reasonably be argued are not to the detriment of the honor or interests the political unit they are leading. However, it fails spectacularly when that condition does not apply.
From a Krugman op Ed (during a government shutdown crisis, but I think the point is timeless):
this is no laughing matter: The cult of balance has played an
important role in bringing us to the edge of disaster. For when
reporting on political disputes always implies that both sides are to
blame, there is no penalty for extremism. Voters won’t punish you for
outrageous behavior if all they ever hear is that both sides are at
With today's proliferation of media and pseudo-media outlets, conditions may be changing. A lot of newer media outlets are starting to reject what they call false balance. A bit of that is starting to leak into more mainstream outlets, but organizational culture there does not change easily.