There are two camps: the we-should-just-use-irc camp, and the we-need-every-feature camp. You fall in to the former, and I would bet that a lot of people here fall in to the former.
However, many people fall in to the latter, and Slack handily beats the competition there. There is also an element of having nice and polished features baked in that appeals to many people. Want it on your phone? There's an app. Want to search? Baked in. Want convenient chat bots? Click a button.
To be sure, all these things are possible in IRC and other lo-fi chat protocols, but getting them set up is easy on Slack. I see this as similar to the argument of Linux vs. OSX. Linux can do practically anything OSX can, but it requires tweaking and setting up. It's a battle of pick-and-choose vs having it all baked in.
However, many people fall in to the latter, and Slack handily beats the competition there. There is also an element of having nice and polished features baked in that appeals to many people. Want it on your phone? There's an app. Want to search? Baked in. Want convenient chat bots? Click a button.
To be sure, all these things are possible in IRC and other lo-fi chat protocols, but getting them set up is easy on Slack. I see this as similar to the argument of Linux vs. OSX. Linux can do practically anything OSX can, but it requires tweaking and setting up. It's a battle of pick-and-choose vs having it all baked in.