"My ENTERPRISE runs on WhatsAppp/SquareTeams/Discord/Slack" etc etc....
Of course that works until that "enterpise" needs to send invoices, and get invoices.
Bush Jr. started doing that. I recall seeing protestors who opposed the Iraq invasion being arrested for dissent. Remember Dixie Chicks? Yeah, they got cancelled for that. And, lets also not forget about the random violence against anyone remotely kinda like an Arab, to include Punjabis, Liberians, Somalians, Burmese, etc.
I feel like waaaay too many people forgot about post 9-11 shit.
Email is federated, it's just not really a medium people want to limit to 500 chars...
Nothing at all stopping you from writing a client that only allows 500 char messages in and out.
Someone even built a chat system that used email under the hood.