While many people now have smartphones, most people still treat their smartphones like feature/dumb phones. They haven't properly set up their contacts with email information, or put them in the cloud, so sending someone an email from their phone isn't as convenient to them.
Also, they may be used to sending to other people that don't have smartphones, and therefore don't think of emailing them pictures because they figure they can't get them on their phones that way. They're conditioned to use MMS.
The technology may be nearly mainstream these days, but average people have yet to catch up to it. I'm still teaching people how to manage their contacts when switching over to smartphones. We see it in posts on these forums all the time. Some folks just don't get it until it's spoonfed to them.