I had a globally distributed family and WhatsApp was literally a life changer for me back in 2009/2010. I'm sure other people in a similar position will also k

I had a globally distributed family and WhatsApp was literally a life changer for me back in 2009/2010. I'm sure other people in a similar position will also know what I'm talking about. It was super lightweight, cheap, multiplatform - when I was interning in Singapore in 2012, I was able to stretch a 2MB pay as you go SIM plan over 2 months using WhatsApp over WAP on a Symbian iPhone. There are few things I will be more loyal to. Now, with my biases declared, I am genuinely open to understanding why SMTP/IMAP based chat didn't take off. I don't know much about the protocols but as you say, email should have solved this problem. But somehow it lacked that immediacy of instant messaging that made me feel that much more connected to my family halfway across the planet. Maybe that's what it was - email delivered in 1-5 seconds is completely fine, but instant messaging needs to be delivered in under 500ms ideally. Is there something about the email protocol that makes it slower due to some tradeoffs?