I can't speak for Zach, but in 2019 on The REPL podcast #23 (https://www.therepl.net/episodes/23/), at 00:41:01 and 00:45:31, he talks about being a bit unhappy with how the core team communicated about his arity-optimized vec/hash class proposal.
He then talks about Aphyr's and Chas Emerick's similar experiences, and laments how in the earliest days, it was still possible to contribute, and how when core development closed off, it was never articulated up front until "Open Source Is Not About You", which is its own can of worms.
Overall, it's a good and nuanced discussion, but it's obvious he wasn't in unreserved love with the language, so I'm not surprised he left.
Yeah, no, I'm not saying Zach wasn't unhappy with the whole core team vs Emerick drama, none of us were. I kinda get it, but also, I don't get it like at all. There are so many tiny details I don't know anything about, but I also feel it was somewhat personal, not really socio-technological (so to speak). Otherwise, we would've maybe seen a big split and a Clojure fork. I see the similar tension (for years) now in Emacs and Org-mode camps. Contributing to core Emacs has similar pain points - specific workflows (no PRs - patches discussed in the mailing list, tone of dismissal toward community-submitted fixes, etc.), but I don't see any big contributors going like: "fuck it, I'm tired of this BS, I'm gonna go contribute to Neovim instead..."
It is really sad that Chas decided to leave slamming the door, makes it almost impossible to imagine him returning and contributing to let's say to Jank, which afaik has none of the hurdles he complained about.
He then talks about Aphyr's and Chas Emerick's similar experiences, and laments how in the earliest days, it was still possible to contribute, and how when core development closed off, it was never articulated up front until "Open Source Is Not About You", which is its own can of worms.
Overall, it's a good and nuanced discussion, but it's obvious he wasn't in unreserved love with the language, so I'm not surprised he left.