It's a bit anecdotal, but I imagine Slack is being careful because they are targeting businesses. Discord is a similar platform which iterates new features extremely quickly.

If that is the case, Slack should want to maximize features, even to the point of excess redundancy, so users can tailor their business product to the specific needs of their business. People don't work productively being boxed into one way of doing something, people work best if they are free to find their own ideal way of doing that thing or are able to tailor the product to the unique tasks they work on.

Think of all the different code editors developers use. Some are straightforward, some have a steep learning curve, yet the good ones are good because users can customize them toward their own personal preferences.