I must've missed the memo which says any conversation around the globe is waiting for my input before it proceeds.
But you may have missed the memo because you're in the wrong time zone, and with Slack, your possibly-relevant input is ignored because you can't participate in real time.
This is my beef with chat. As the OP says, it biases all conversation to those in the same time zone. Fine for some things (like baked goods arriving in some far-off kitchen), but not for others (like a design decision that should have input from stakeholders around the globe).
But it's often used for the reverse.
If my org takes pride in consensus for everybody, everybody needs to have the time to submit input. It's not uncommon that some active users in a chat go for an ad-hoc decision just because they are more than one and want to work _now_. In the long term this damages the culture, splits the participants and is difficult for newcomers.
I gripe because I am a US left-coaster who works with a team that is increasingly based in Western Europe. By simply deciding to rely on Slack, they have essentially cut me from development conversations other than the weekly live session.