Maybe because, the cli mode means, you need to remember the commands?
In GUI mode, though inefficient, you know exactly where to access help and a few basic params (like dropdown menu on top, usually save under file, cut and copy under edit) that smoothens the learning curve. They have some solid ground from which to start exploring.
Whereas under console mode, there is no unifying paradigm. So each tool has a different way of doing the same thing. There is a lot of inertia at the start. Like what command is it for help 'h' or 'h?' or 'help' or 'H' ? What command is it for quit 'q' or 'quit' or 'ctrl+d' or 'ctrl+c' or 'bye' ?
For example, in gmail, I expected archive to be 'a' and delete to be 'd' or atleast "DEL". Very basic operations and basic expectations. Turns out, archive is '#' and delete is some char I can't remember now (I think '{' and '}' to indicate whether to go to the previous mail or the next mail. A 'd' to go to next mail and a 'D' to go to previous email would have been a lot more intuitive). Of course, you can customize the key bindings, but then you got to go do it across all your accounts.
While people may be quite happy to be able to wield so much power within the slack environment, they are very quickly going to lose their enthusiasm with the introduction of each new console tool, unless what they have learned in the slack environment translates into easier learning curve in the next console env.
Basically for users to be able to adopt the console mode, there is should be some sort of standardization.