This has been noticed before here - there were at least two lengthy threads about the Las Vegas mass shooting and the perceived lack of coverage. No conclusion was drawn, but a common suggestion was that as the shooter was well outside the norm (old, rich, no motive found) and there was a lack of photogenic victims the case was too "difficult" to present.

A personal opinion is that, as there appears to be no political will to even attempt to understand mass shootings (never mind try to prevent them) a pall of defeatism has descended. If 58 people being shot dead can be played down, 7 people being shot dead will be ignored. I wonder what death toll would cause a difference.