Last legs? Maybe, but he played 16 games in 2018 and 2020. Players can and do have bad luck as far as injuries go, get your arm caught in a pile up of players, etc. and anybody can get hurt. I'm not saying he's the player he was in his prime, but it's not a slam dunk that he'll get hurt again.
And "what has he ever won"? Defensive player of the year 3 times, for one. If by won you mean SBs, no, but as we all know it's a team sport. As far as why he went to the Cardinals, they do have a Pro Bowl quarterback, receiver and safety. The team finished 8-8, certainly with the loss of Hopkins and very possibly Watson, seems more likely the Cards will make the playoffs than the Texans.
I do think he was overpaid, that's pretty obvious. And he may just have gone there because it was the only good offer, we don't know.
Just saying we've seen players thought to be washed up go to other teams and rejuvenate their career, we'll see what happens...