This crime is the worst mass shooting in the history of the country perpetrated by a white man and yet there is no drumbeat about domestic terrorism, white supremacy and the usual memes of the left. Why? Our rulers are hoping the people will got distracted by something else and just stop asking questions.
Those are common Leftist points, and you bring up that they are conspicuously absent from the discussion. That may well indicate that they have some idea (or more) telling them who is and who is not involved. That they are trying to keep politically inconvenient sentiments from surfacing and being expressed. That they are doing the usual "not terrorism" dance even without facts. All point in the same general direction.
They do not (ever!) want to be put in the position of apologizing to anyone on the Right. Which means look left, because they don't want the blame to fall over there and will do anything to protect Leftists or Islamists from direct blame. Anything inconvenient to the Left's victimhood will likely be suppressed or show up in very fine print somewhere in the back of style section.
There remains the possibility that this is the sole act of a nutcase, but the sheer number of firearms present makes me think other things were afoot.