also rules out usecases for people who aren't actually "settled" and have to follow social norms in some areas- actually expecting a girl to contact me via phone or email before the first date, i'd be living in a fantasy land. it just won't happen
Also IMO it's a lesson I give for free to my contacts because I explain why I do not use such services.
Yes, I have occasionally missed out on things as I don't use Facebook, WhatsApp, etc.
However...
I find that instant messaging enables and promotes poor organisational skills in colleagues. Rather than processing tasks in a timely and professional manner, they have a safety net of being able to send a group message at 23:30 the night before a meeting the next day. I also find that instead of a well planned, concise email, these people will spam colleagues with a string of brain-fart messages until, 60 minutes later, a consensus is reached.
Funnily enough, when there is no option for this, people never have a problem contacting me in a professional way.
The problem in that sense is that people do not know other system exists. Not only "casual people" but technician do not know them. Often I find programmers (not code monkeys, not stupid people, not "ignorant" one) that do not understand how my Emacs works, for them seems magic. Many when I say that I have RSS via mail, notes from mobile (BlitzNote) via mail, projects&c via mail they think it's impossible to handle such volume of messages, when they see a modern (ancient) MUA the seems child looking at some incredible machines.
IMO the sole solution came from a state-backed action that start to limit actual IT trends for the sake of democracy, competition and national safety and empower universities and schools enough to teach basic IT concept not in term of ridiculous "coding courses" but in terms of IT freedom and dangers like democracy vs dictatorship in politics.