Actually the "why" is VERY important. Especially to gun owners. The slippery slope of "He just had mental illness" gives the anti-gun people ammunition in their fight to keep guns out of everybody's hands. Here's how:
By saying that everyone with a mental illness should not own a gun allows someone in a government capacity to dictate a "level" of mental illness that determines a threshold for allowing gun ownership to some and not others. This means continued access to health information that should be privileged information (HIPAA law). Now, I'm not saying that someone with a profound mental deficiency should be allowed to carry, QUITE THE OPPOSITE. Obviously, this guy has skimmed the surface of police awareness, but not to the point of a federal notice. This dude is in his mid 60's. Something made him snap - this type of behavior, combined with the ability of assembling a cache of automatic weapons can't stay off radar for that long. But, even though he may have "snapped", there is a LOT of fore planning that went into this - transporting a large cache of weapons to your hotel, getting a room with a high enough vantage point to be concealed, but still have high enough caliber weapons that would still be that effective at that distance, etc.
As
@JSJJ388 mentioned, those people were fish in a barrel taking on indiscriminant fire from an elevated vantage point. I'd be willing to bet that this guy is former military. His age puts him possibly in Vietnam War timeline.
Either way, I am VERY impressed with the response time of the LVPD. From what I've read, the entire ordeal from initial shots fired to forcable entry into the hotel room was less than 1 hour. That's having a SWAT team deployed, explosives set on entry and take down all planned and mobilized.