It's you that doesn't "get it."
MLB is at the FOREFRONT of live video streaming. They've been doing it for a decade now. In fact, a large portion of live streaming broadcasts that you watch from anywhere are using servers on loan from MLB.
In-market games are unavailable due to contracts with local broadcasters. If your local Fox affiliate has a contract with the Diamondbacks to show their games, they're not going to want the MLB allowing potential viewers to watch games on computers or iPad or Apple TVs. Then you're not seeing any of the advertising, which is what makes it profitable for the local affiliate to carry the games.
If you really want to stream local market games to your phone, just get a Slingbox. It can be had for about the cost of two seasons of MLB.tv or less. That way you watch your local market games, get your local ads, and your local affiliate receives the ratings.
As a Yankees fan living in Texas, MLB.tv is a godsend. And when the Yanks play the Rangers, I'll just watch it on my Slingbox.
And this new model is further proof that MLB gets it. I have been annoyed the last two years that as a subscriber to MLB.tv I've still had to pay just to have the app (last year $30 to get it for both my devices). Glad they found a smooth way to rectify that.