The reason the Packers didn't sell out initially is because they sent out the playoff forms in November. At that time, it didn't look like the team was going to be playing anyway. And if you bought playoff tickets and they failed to get in, you wouldn't get your money back. They just rolled it over to next year. With the holidays close by, that seemed like a risky investment for some people. Oh, and it's going to be like -10 degrees too.
I'm not sure why Indy didn't sell out. The game is indoors. My only guess is that tickets are way too expensive and people didn't want to buy them. Plus, I'd rather watch the game with friends at a big group gathering. I've been to one Colts game in my life. And I don't have any desire to go back. It honestly wasn't that exciting to see the game in person at the old RCA Dome. Again, at home I can watch all the NFL games at once at not have to travel anywhere. Also, I'd rather spend less money and go watch the Pacers play instead.
Had the game been blacked out, I would have been done with buying NFL merchandise. It's ridiculous to think they'd consider blacking out a game because the stadium was only 97% full.