I'll take a guess as to why failure of others is not a more highly revered measure of obviousness or lack thereof.
First, obvious to one of ordinary skill in the relevant technologies is the standard. So, if someone else tried and failed, you'd have to at least establish that they are of at least ordinary skill in the relevant technologies.
Second, the standard is obviousness in view of any prior art references as defined by Section 102. If failure of another is to prove non-obviousness, you're going have to show that they were familiar with all available prior art -- or at least all the prior art cited during examination.
I did not mean this as a failure of another, but rather as failure of many others. Failure of one POSITA is way too weak
a test.
To some degree these are the steps you outline would have to be followed anyway in the standard obviousness test.
Except in the standard test they are done for an imaginary POSITA, whereas if failure of other can be shown, there
are some very real POSITAs who have attempted it, so some arbitrariness is removed from the test.
Comparison of the standard test to the real world I think reveals its flaws. You have mentioned that the POSITAs have
to be shown to be familiar with all available prior art. That's an impossible standard in real life. Obviously nobody knows
everything. And if you look at the way "primary" obviousness test is conducted, it's inevitably skewed by impermissible
hindsight. Because the question is typically "given THIS prior art, would it be obvious to combine the teachings to
arrive at the answer?". That's why I think express motivation to combine in prior art are quite important. Without it
you are comparing the inventor trying to solve a problem (can you solve this problem given your knowledge and access
to trillions of pages of information?), with a POSITA conjured by an examiner/agent, who is instead given a different problem
(can you solve this problem given your knowledge and these few hundred pages of information?). I think you will agree that
presenting only a tiny subset of all available information is a very strong suggestion at the solution.
I am not looking at it from the point of view of "what does article 103 says", which I think makes it obvious that I am
not a lawyer. I am trying to figure out how to interpret article 103 in a way that makes sense

And it doesn't make
any sense to me trying to imagine what a POSITA with all the knowledge in the world would do. May just as well
imagine omnipotent god and declare all inventions obvious

One can also say that having all the knowledge is like having
none of it, since a huge part of problem solving is
making a choice what information is relevant and what information
isn't.
That's why I think that when you have a reasonably large number of POSITAs attempting to solve a problem, and they
did not come up with a solution you do not have to worry about constructing an abstract POSITA. You do not have to
worry about whether the knowledge you endow that POSITA with constitutes impermissible hindsight. The real world
POSITAs will have some of the relevant knowledge in common, some of it will differ, and they will have reasonable skills
in searching for information they consider relevant in light of the problem they are facing. And the combination of all
that will be the *relevant* prior art.
Once you've established that the other is of ordinary skill in the relevant technologies and is familiar with all information that qualifies as prior art, then I'd think that failure of that other would be pretty compelling evidence of non-obviousness.
I guess my view of this is that the "standard" POSITA test has to be conducted to closely resemble
the real world situation when a number of POSITAs are facing the problem solved by the invention. Because
that's in my view the definition of non-obviousness. The problem is that the real world proof of
POSITAs working on something is hard to show in many cases. It's simply not available. But it's as pure a
test as there is.
Although, there's always the possibility that your solution was realized by the other and they just chose not to do it that way -- in other words, the fact they didn't chose your approach might not prove that your approach was non-obvious to them.
Cue in another secondary test - unexpected results

Those are probably some of the reasons it's only a secondary consideration.
Regards.
Thanks for humoring me. It's probably a bit too impractical of a discussion, but I can't help it.
I have to try to make sense of things, my brain fails otherwise.