I think (in general) Slack has been more open to automations and integrations, so entire workflows rest on it.
Teams is catching up in this respect, but fewer people rely on it beyond day-to-day communication. Not that it's not important, but maybe just not as critical to things beyond person-to-person comms.
I disagree a bit: companies use it partly because it integrates with SharePoint, so a team can have a SharePoint folder easily. That often breaks down, because who needs access to that folder almost never maps to the team members, but it's enough to sell it to people to get their foot in the door, and after that they accept the hideous pain of changing it.
