1. He may not have. He's in the twilight of his career, does he really want to spend another year at a club that has said it's not competing? If he opts not to, that's valuable draft pick compensation, which the Cards need to maximize.
2. They've already shed a ton of salary, and as you said he made more than that last season, so even with that $21 million they come out ahead.
3. There are no 1B on the roster anyway, just guys like Burly, Walker, Gorman, who would be projects at the position. It's not like they'd really blocking anyone who is primed to take over. And the QO deal doesn't come with a trade clause so you could always flip him for some kind of prospect return.
I get the decision, but it definitely points to a longer rebuild than a, "maybe we take a year off and then are right back in it in 2026 or 2027" situation.