I guess it's just my anecdotes, really. I find Slack search to be horrible because there is no grouping of conversations. For example, many times a day several people are trying to have several different conversations in the same channel. Reading through that afterwards is a mess.
Basically, as a software dev I don't think there are actually too many things that need to be answered "right now". If that's the case then I would think there isn't enough planning involved.
Well there might be the context you're missing. You're looking at this as a software developer. I can tell you from a ops standpoint I get blocked daily just because of some small information missing/needed to be checked. Slack solves this. (If you're in the same timezone... Which is not always the case and slack falls apart here.)
Basically, as a software dev I don't think there are actually too many things that need to be answered "right now". If that's the case then I would think there isn't enough planning involved.