Phoenix has a large market if you look at sheer numbers. The problem is that Phoenix has millions of transplants. A benefit for Phoenix, though, is that no type of sport has really grabbed the Southwest yet; college football and college basketball (the Carolinas) are huge in the Southeast, but the same can't be said for the Southwest. So, professional sports could do well in Arizona if owners and leagues did their research and figured out how to get the population on board.
I also found it strange that no one tried to grab the team and move it. I know that in Madden, I would take ownership of a second team and then move it, then build the franchise from the ground up. (I could also raid the team for franchise players and draft picks if I had a bad season with the Eagles.) The Cardinals were always the obvious team to move. Why this never happened in real life doesn't make sense. The team didn't even have its own stadium for over 15 years! They rented Arizona State's stadium until a couple years ago. (On a side note, anyone else think it's funny that the Cardinals finally get their own stadium, and now their own stadium bears the name of a university?)
Norman Braman actually wanted Philadelphia to build a new stadium in the 1980's so badly that he threatened to move the team to Phoenix, before the Cardinals moved there. The city called his bluff, and he never did it. Of course, Braman was one of the worst owners in Philadelphia sports history (he let Reggie White go, among other things), and he just didn't care enough about the team to actually go through with moving it. He usually just went vacationing in Europe and let the team fend for itself, hence his nickname of "that man in France". In the early 1990's (after the expansion bid voting was done, apparently), Braman finally sold the team to Jeffrey Lurie. Ealges fans celebrated that.
The Cardinals aren't going to be moving any time soon, for many reasons. On top of having a new stadium, Phoenix is now going to be/already is one of the better locations to host the Super Bowl in. This is also one reason why the NFL wants a team in Los Angeles. On top of a market of 15 or 20 million people to have as a fan base, a Super Bowl in Los Angeles in this day and age would be huge. Look at some of the recent Super Bowl hosts. Jacksonville? Detroit? These cities just can't compete with obviously great cities for fans to come to and cities that have all of the amenities, like Miami.