Encryption wouldn't do you any good in this case. They're looking for who you are contacting, not what you're saying. You'd need to move all telephony onto something like Tor to get around this (and your ISP could still tell what end points you were connecting to, when you were connecting to them, etc).

Real-time synchronous communication ( like phone calls ) is pretty hard to hide, it uses bandwidth and takes up space on switches and needs low latency to work at all ( make a voip call to someplace that only has satellite internet to see how bad it can get ). If you're serious about hiding your communications; either build physical networks that you control and limit the amount of traffic visible to the public network ( i.e. trunking calls ) or send messages steganographically encrypted in pictures of your cat you post on Facebook.

Because they see no real market effect for 'real personal security'. People do care about privacy & security, but they don't physically understand how something like OTR works. Things like banking & tax apps putting in fake progress bars to make the app feel like it's 'more secure'. Or apps like snapchat that remove access for the standard user, but still leaves them on the phone after they are seen. Or your standard home lock.

Sure, but how much effort would it take to link in libotr if you're making a chat client? Not much, and, if it's popular, the gains are enormous.

It's not just link, it's also integrate and not effect performance and UX. Many of these apps are mobile & cross platform and have things like message sending to clients you've never connected to. Messages getting restored by the server if you re-install the client. Push notifications by another server, saved history and so on. Could it be done in a hackathon night?