Even now, some fans are thinking that the Cards are going to get a Sunday Night Football game.
The only way to guarantee a nationally-broadcast home game is to make the playoffs. The NFL doesn't care about the Cards' new stadium, and national fans certainly don't either. The reason that the Lions got an extra game was because Detroit has a significant national following (I still see Barry Sanders jerseys around) and people will watch them. Same with Dallas. If your team becomes a national institution, you'll get broadcast games even when you're bad because people will watch them (watch the Packers get a nationally-televised game or two). But when you're stadium is regularly half-full and your games haven't been honestly sold out in a decade or more, you're not going to get a lot of love.