There are so many issues that have to align for SNAs to clear I'm surprised any do. Not only does the SNA Pool inventory have to be available (and is not shown on SPG.com), the same room must be available for the duration of your stay (again not shown on SPG.com). And you have to be at the top of the list for the system to apply the SNA. It is a "black box" process with no disclosure about where your request stands and there is no apparent means for anyone to intervene. Now, on the up side, many have reported having their SNA request denied only to get a Plat upgrade at check-in.
So, no real "conspiracy theory", just questionable implementation. The more transparency put into these programs make them much more valuable.