As has been answered elsewhere in this discussion:

That was over 7 years ago, so not particularly recent. And you can get the auto-promoting behavior with +' instead.

I don't see how a change could be much more minor, honestly.

It is a breaking change, that sort of change could introduce bugs into existing codebases. If that matters, you can't upgrade your Clojure version without careful change management anyway.

It isn't like reduce is being depreciated or something. I don't need to change how I think about the language.

A breaking release over 7 years ago, doesn't mean that having no (as far as I know) breaking changes for the last 6 years is any less impressive.