"we may never fully know..." UH... yeah, it's no secret. I know and I'm trying to help you know, so that "we can fully know". I know all the people that created it and I worked with them on 2015, 2021 and already starting on 2024 If you're looking for hidden agendas, they aren't there. It's collaborative work by many different parties.
I'll try one more time to explain why the 2018 change was important.
This has nothing to do with approving a post cap. It has everything to do with approving a post height from a table who's engineering is only based on a 2 ply beam max span, and the maximum trib area that can be created, and then also approving a post cap to bear a three ply beam which can be sized by the code. It was a mistake in the assumptions made that a 4x4 would always only carry a 2-ply beam. A code user that does not realize the derivation of the maximum 4x4 height would not have been prompted to question it supporting a 3-ply for any reason other than the beam bearing. Such as:
"OH! you have a tested post cap for that 3-ply beam on a 4x4. No problem then." The problem is there is a problem, but it's not the beam or post cap. It's the load on the post from a three ply beam (and resulting trib area) that may now exceed what the post sizing was based on.
This is not anywhere near engineering necessity. It's a tested post cap.
I don't really know how else I can explain this. Its the inherent difficult of created pre-engineered tables. Assumptions have to be made, but they also have to be known.
Truthfully, deck codes are a brand new work in progress in codes that have been in works for over a hundred years. The 2015 and 2018 provisions should be thrown away as trial and error that has brought us to the 2021. When 2024 is done, I will say the same of throwing away the 2021. It is going to take a few cycles to plateau at a complete prescriptive set of deck structural codes.
Again, happy to answer questions, but I'm starting to feel like maybe you've already made up your minds. If you had seen my visual presentation in my recent webinar, I think you would fully see whats going on.