I think the reason why this dead horse has been around for 80 pages and is still going strong, is that the autopsy is far from complete and evidently, nobody really knows what the horse died of.
Meaning, it's still very obscure and unclear why this particular test was performed.
Nobody could have possibly believed that a surprise test in the form of a nasty surprise laid on would-be standy riders - at the very moment when they thought they would be entering the queue for TSMM - would be in any way useful, informative, educational, helpful, or especially that it would be cheerfully received.
I'm baffled at the bigger trend that the test seems to indicate. I don't understand how "reservation only" seating would work with rides at a theme park - which despite our love for it, is after all just an expensive and lavishly-designed version of an amusement park or carnival midway ... as if they were scheduling dining on a cruise ship or something.
But even if you COULD make an argument that this is a good way to go, how could anyone possibly think that a "gotcha" surprise is going to be even a tiny bit successful, when the subjects of your test (paying customers) are (a) not informed of the test until it is too late to back out, and (b) have formed their expectations of the way that the queues should work from literally a lifetime of experience at WDW, at amusement parks and midways.
I have only 3 theories ... maybe these should be presented in the form of a poll so you can vote on them, but you would only be guessing anyways unless you've been present at fairly high-level meetings inside the Disney Corp.
1) The decision maker on this test is really out of touch and had no idea that it would baffle and anger a lot of people, especially the would-be standby riders, but also non-park visitors who would naturally hear about this "test" online within minutes or hours, and who would of course mostly get a partial, second-hand version of the events.
2) The decision maker is not out of touch, and knew that this would baffle and anger some of their guests, but thought that a little bit of "tough love" is necessary to kick people out of their rut of old-WDW, old-amusement-park thinking and drag them into the new era of boutique, reservation-only theme park touring. Or else that the bad feelings they would cause during the test are "worth it" for the greater good of getting solid, real-world test data.
3) The decision maker is not out of touch, knew that it would cause ripples of mayhem, but did so deliberately because they're not a fan of the way things are going. They don't have the power to make serious changes to the system, or to gather data with a fair and unbiased survey, but with the limited power they have over one ride or one park they decided to give park visitors a full dose of "this is where FP+ is going" and then let the visitors' complaints speak more eloquently and effectively to upper decision makers than they would ever be allowed to do.
Your guess is as good as mine ...