The other thing going here is that Butler hasn't had a lot of time to develop and I'm not sure how much, if at all, he was allowed to practice with the team after being put on injured reserve. Difficult situation to be put in when you've got a rookie coach and a deep position group ahead of you.
That said, Arizona has a pretty terrible recent history of bringing in expensive veterans who don't pan out while watching younger guys they release go on to be successful for other teams. Here are a few examples from this last offseason:
Cardinals signed Michael Crabtree last year, paid him over $2 million and proceeded to cut him a few weeks into the season. Terrell Suggs signed a 1-year, $7 million contract and then asked to be released during the season so he could "play for a winner." They cut Josh Bynes, one of their better defenders who was in his first year of a new deal but coming off an injury, and watched him do pretty well for Baltimore (Bynes certainly outperformed the guy that replaced him in Arizona).
I get the impression that their front office/GM is getting nervous and in need of some immediate success. They have had success in the past bringing in vets when they had an experienced NFL coach in Bruce Arians at the time. The Cardinals may have been Bruce's first full-time head coaching job, but he was named the NFL coach of the year with the colts as an interim and had won a super bowl as a high-level coordinator a few years prior. Even then, I don't think they had a sustainable culture/development strategy as they fell off from their super bowl year pretty quickly. I really just don't think prioritizing veteran free agent signings will work well with a coach that is completely new to the NFL who wasn't all that successful even as a college coach.