For the longest time, I recall the opposition to async/await support being twofold:

1. adding support would require deep changes across the CLJS compiler (theller, creator of shadow-cljs, once tried and concluded this)

2. macros from libraries like Promesa provided similar convenience

There were some other arguments brought up at the time (e.g. just use core.async, expression-oriented languages aren't a good fit with async/await, etc.), but they were usually specific to one person rather than something you'd see repeated in forums.

In the Clojurians Slack, borkdude once stated he wasn't convinced it'd be impractical to add support. It seems that he eventually took the time and made it happen. Extremely thankful for that.