One question I have not seen answered was why so damn many guns in the room. It makes no sense. Ammo yes. Loaded mags yes. But that many guns not so much.
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I can only speculate that he had tried to use a bump fire stock prior to this and found they were prone to overheating guns and leading to jamming. Instead of clearing a FTF or FTE just throw it down and pick up the next one. My 2 cents worth which on the interwebs is worth even less. 
bob
I agree.
Considering his accounting and audit background, my gut feeling is he went out in the desert, used a stopwatch, and timed his effective sustained ROF with a bumpstock. He also probably accounted for the rifle heating up beyond what he could tolerate, and because of the time to reload or possible jams, he figured ROF / 100 round Surefire magazines, and x% of stoppages, meant that setting up umpteen rifles got him the most amount of rounds in the 10 minute window or whatever he thought he could shoot for, and still evacuate the hotel as just another "fleeing guest". So he could go on and do phase II with the Tannerite and the other rifle he'd left in his car.
The cost wasn't an issue because of his financial situation, nor did he care because his escape plan seemed predicated around being able to do more attacks, and/or having an "escape plan" was just a mental placebo to get him to commit, and he knew he was going to die all along.
I further suspect when he was actually shooting from his hotel suite, sticking with the same rifle longer was just easier, and despite filling the room with the rifles, he didn't decide to use them, adrenaline or whatever.
