I suspect the thinking is that, if the show proves somewhat successful, they'll use the introduction of Hal, John, and/or Kyle as a way to drum up excitement for the second season.
There's also the distinct possibility that this is already the planned, but they want to save it as a surprise.
Well, hopefully for Green Lanterns' sake, the show will work out, otherwise, I kinda' wonder what will happen to it. How much of a shellacking can it take with no real hits under its belt? A long time ago, one of my favorite video games was the Wing Commander series. It was way popular about 1000 years ago, even to the point where it got its own movie. Then the movie came out, everybody hated it, and...you just more or less never heard of Wing Commander again...even to this day. It's actually kind of amazing how thoroughly Wing Commander was suddenly swiped off the map right after being one of the biggest names in PC gaming.
I guess what makes me think about this are the names attached to it, and leaving out the most popular characters is also a questionable decision. That, and I think Green Lantern is probably an especially difficult IP to do justice in live action. I know they have a big budget, but having the right vision matters a ton, and I'm not sure I'm confident that the people behind the scenes do.
^^ What was that from and why would Parallax have a GL ring?