If you dont like seeing people face to face and you still need to communicate with team members slack has the ability to be flexible enough to communicate many different ideas very accurately. With bots and file sharing slack is the one stop collaboration board (along with google docs for co file editing)
and for people that are social or non technical slack has that friendly feeling ... its has taken exactly what we have been hoping from the internet , efficient communication and sharing and made it be homey instead of cold.
Slack is just another message board for tech guys but to the rest of the people tech guys have to communicate with (and would want to make this communication as fast and accurate as possible) slack is a world of difference from other chat services.
They took good tech and added the human touch.
I think it would be far more accurate to say that it's due to a lack of other products that as easy to use for so many.
I've considered putting my internet savvy parents on Slack, and they are well into their retirement years.
I don't think Slack is addicting as much as most humans enjoy contact with other humans. We are wired to be social. It helped us survive and thrive. Slack et al is simply a symptom of that wiring.