Define older models. The only Airbus models that I've seen with that placard had energy-absorbing seats installed like in the EC130B4. Its required per the Limitations section in the AFM. The AS350 doesn't have that requirement unless it has the pilot/co-pilot E-A seats installed but the only placards I've seen required on that model are on floor loading. Besides the original 350 bucket seats had storage compartments incorporated into those seats as well. So perhaps your placards were for a different reason as the area under the aft factory seat was used for storage on a regular basis in my experience and was perfectly legal. No different than the EMS interiors.
You'll find the majority of AS350 EMS interiors flying around the US are of the same layout. And with the same amount of equipment stored in various locations. I don't know how the EC130 EMS interiors handles storing items under seats but the 350 has zero issue with it from a regulatory side other than they should be restrained in some manner from my experience.

Why did the helicopter crash?

Mechanical failure....pilot error?

Any information out that begins to address the cause of the crash?

Daytime...decent weather....windy....and it crashed during landing.....so what went wrong?

Another ASplat hydraulic problem?

Well, this particular machine had dual-Hyd, so bet something else…

Engine failure? All the parts looked to be right next to the aircraft cabin and fuselage?

Main Rotor blades did not seem to show much rotational damage on the leading edges.

Same for the Tail Rotor Blades from what is visible.

It was windy....but they were landing at the airport....not some confined area.

Christmas Valley is pretty much out in an open Plain....no mountains very close as I recall.

News reports are saying the landed hard then rolled over.

Seems some folks are being pretty tight lipped.....even the pprune Accident Investigation Crowd.

NTSB prelim confirms pprune posted information. And nothing more.

Any logical reason for the NTSB not to travel to the crash scene?

Would not that be a great place to initiate an Accident Investigation....survey the location of all the bits and pieces....photograph everything....identify any witnesses...locate security cameras and that kind of thing?

You'll find in a number of non-fatal accidents the NTSB will not travel and delegate the FAA to perform the investigation. A NTSB IIC is still assigned to oversee the investigation, determine the results, manage the reports, etc. The same investigative steps are still performed and usually by the same people in these types of events. However, there seems to be an increased use of this delegative authority with the backlog from covid.