The issue here is that these well-meaning Cardinals fans have employed an arbitrary end point to try to mask a more meaningful sample of data. Every end point is arbitrary, technically, but some like a 16-game stretch, or one full season are in common usage. No one's ever found any meaning related to a 11-game or 12-game sample.
You can probably guess what happened in the games before that. The Cardinals, in fact, only started that 10-2 streak after a six-game losing streak. If you look at their 12 previous games before the 10-2 stretch, the Cardinals were 3-9. And if I really want to be a dick and employ arbitrary end points myself, I'll note that the Cardinals were 3-15 in the 18 games before that 12-game stretch.
The more you think about this, it doesn't make much sense. The idea behind noting that the Cardinals are 10-2 in their last 12 is that the Cardinals are secretly a great team who will keep up their excellent record going forward. Why then did the Cardinals, who went 3-9, suddenly get better and go 10-2 in their next 12 games? Why did that totally arbitrary win-loss split that had no meaning when the Cardinals sucked suddenly become meaningful now that they're apparently great?
If you want to know why the Cardinals have been 10-2 over the last 12 games, there is a simple explanation: They've won virtually all their close games. Ten of those 12 games have been decided by a touchdown or less, and Arizona has won nine of them. They've basically been the Baltimore Orioles of football over the past 12 games. If you want to count on that happening over the next 12 games, be my guest.