This is a rare case where things are inconvenient for nerds to use, but more convenient for ordinary people, who tend to be more comfortable doing stuff on mobile platforms than nerds are.
Is that also true for professional use? For private use/relatively few threads I'd agree with that, the insistence on IM on desktop is a niche, but I'd think most people using chat a lot professionally (e.g. Slack) do not use it mobile-only. And if you'd want them to shift communication away from e-mail, it gets even more important.
(as p49k alluded to, iPads help, but few professional users have them as the primary device)
