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.