C. A. R. Hoare
I listed a number of solutions, all built by different people, at different times, in different orgs, and some of those solutions (OAuth, SASL) being much more organic in how they evolved, and yet all are ultimately large and complex.
I think that hints at the problem space being... large and complex and requiring large and complex solutions.
What we _can_ do is avoid adding complexity unnecessarily, but what looks like a simplification today (e.g., picking the best current encoding system) might look like a terrible mistake in twenty years.
Of course, SSL 2.0 did reference x.509, so hey, SSL 2.0 should have invented its own PKI. Except that Netscape might have come up with something terrible that worked in 1993 in labs but didn't scale to the web, or just full of security problems, or...
What you say sounds nice and right right up until you actually look at the details of what actually happened in real life, and how things actually evolve when they have little standards involvement.
Was the IETF PKIX WG "forcibly" shut down, or it merely concluded, with new WGs popping up to do similar things when needs arose?
First, anyone can participate. The only cost is the value of your time.
Second, yes, there are the usual suspects -- the ones who've decided to spend a lot of their time on whatever the area of tech we're talking about.
Third, working groups have charters that delineate what RFCs they will publish. Sometimes the work runs out. Sometimes the people run out of energy. Sometimes the tech is 'done', at least for a while. Then the WGs shut down.
Fourth, sometimes new work gets brought to the IETF in an area where the relevant WG has concluded, so then a new WG _may_ get spun up to take on that work.