It seems to me that the next step in email should logically be video mail.  It's a wonder why I can't currently just login to my email, press record, record a video message, and send it off to my friends via email.  The technology currently exists, internet speeds are now fast enough so why isn't this popular yet?

I'd say it's not popular because the free email services like Outlook, and Gmail haven't been designed to do this. 

If I want to sent video mail how would I do it? 

There are a couple of paid services that all you to send video email.  Services like http://mailvu.com/ and https://bombbomb.com allow you to easily send videos for a price, and they are a bit expensive.  These services don't truly integrate email and video.  For example, when you use Bombbomb to send an email, the email that is sent actually contains an animated image that shows a couple of seconds of the video and a play button.  Pressing play takes the user to a site that contains the entire message and the video plays.  This is not exactly integrated video. 

There are a couple of free options for sending video email.  My favorite is to use the Viewedit extension for Google Chrome.  This extension allows you to quickly and easily record short messages that can then be added to Gmail with one quick click.  It adds an image to your email that when clicked takes the reader to a site that plays your video.   It can be found at Viewedit.com

Alternatively, you can record your own video with your webcam software.  Save it to a cloud storage site like Google Drive.  Attach it to the email or add a link to the email.