What you have is people using a tool for different objectives, and when their chosen behavior hinders your objectives things seem out of whack.
I'm against shoving an eye of sauron communication hose down people's throats. I simply give my constructive feedback after the fact. E.g. when someone dm's me I say, "so-so is waiting for this to be done for their thing, so mention this part in the channel." or "the other team would need to know this for a refactor, so add this info to the wiki." If someone feels the need for dm'ing for some psychological safety so be it. But the cost of that safety is additional communication overhead for filling in gaps that the person should be ok with. And the people that value the psychological safety they gain usually don't object or have no grounds to object to a duplication of communication to fill those gaps when someone points out those gaps exists.
