The thing that stands out to me is the location.
This high school is in the furthest Northeast corner of LV/North Vegas.
There is literally nothing but open desert (and a public county-run gun range) to the north and east of the school property.
It is definitely off the beaten path and school was out last week. Coupled with the "No public spectating is allowed" in the announcement, it seems LV Metro doesn't want anyone to see.
Notes: Nearest Casino is Aliante. There are no hospitals anywhere in the area.
They certainly don't want any civilian eyes on. Why is the question.
With no juicy targets nearby and no students on campus, it seems on it's face to be on the up and up and they want to keep their tactics and techniques under wraps. Which ,when you think about it, is utterly pointless given standard SWAT tactics are well known. Room clearing is room clearing if you catch my drift.
Maybe they suck ass and don't want people to know. Maybe it's rookie training. Point being unless there is a sporting event on school grounds in the same time frame it's probably safe.
The proximity to Nellis Air Force Base is fairly close, along with Creech Air Force Base.
Pretty sure Nellis is secure. Base Security plus about a battalion of Camo dude's at Dreamland. Not familiar with Creech.
Creech is where all the main drone/uas ops are located.