Truth: The larger the company, the more abundant the silos, and the more disjointed the communication. This is because people and teams have personal preferences.
We have Slack at work. I personally love Slack. Not everyone at our company loves Slack. Some people hate Slack.
As a result, Slack is great for communicating with the people at work who use it. But because not everyone is on Slack when they are at work (i.e. the Slack Haters), overall communication is worse.
How to fix it
The solution is simple: mandate that everyone must have a Slack window open while they are working, and ban the use of other team-based messaging or communications tools.
In other words, declare a preference at the company level and take individual preference out of the equation.
One team likes IRC? Too bad. Another team prefers Skype messaging? So sad. You may not use them for team communication. You must use Slack (or whatever the company has decided is the best tool).
I know that would piss off a bunch of people in the office, but without a unified messaging tool that everyone uses exclusively and ubiquitously, communication suffers.