I can't speak to what he meant, but if I were to guess, Zephyr isn't necessarily that easy to wrangle into shape for PlatformIO so despite a lot of initial enthusiasm and optimism, progress has been a bit disappointing.

As for why, it is probably because MCU makers are a bit nearsighted when it comes to the software side so you get little or no help from there. The strategic decision makers don't understand software. (That's not my assessment, by the way, but that of people I know who either work for one of the major MCU makers or has worked there).

So they do their own thing, they don't do it particularly well, they don't see that they don't do it particularly well or why it is even their problem. I also think that they are a bit afraid of common tooling - possibly because they think it is giving up control or robbing them of the opportunity to differentiate themselves (which is tragically funny since most can, at best, hope to be no worse than the competition).

You'd think that if lots of players can agree on using Zephyr it shouldn't be hard to make them agree on supporting sensible common tooling (akin to PlatformIO), but then again, these companies don't really get software.

(I was tempted to say "modern tooling", but then I remembered that I hate it when people use the word "modern" so Dobby had to iron his hands and delete it).

Most manufacturers seem to have abandoned trying to support them, their community has slowly disappeared, and you can see it.

They seem to only care about Espressif these days.

Zephyr support has not been updated in ages (2021)

Patches submitted to platformio arduino to add Giga R1 support have gone unreviewed for years (I get poked every so often because i did some work on it, so i see the github comments).

The only things that seem to be in okay shape these days are ESP and STM32.

Given the other options at this point, it is nowhere near as useful as it used to be.