Currently, the following potential starting QBs are scheduled to be free agents in 2018:
Bortles
Bridgewater
Stafford
Bradford
Cousins
Garoppolo
McCarron
Derek Anderson
Haha, just seeing if you were paying attention on that last one.
Some, most, or perhaps all of them will be extended this season, but at the same time, some others may become available.
Aside from Stafford, some people will have their doubts about all of them. But unless the Cardinals think there's a good chance that one of the QBs in this year's draft will become a long-term starter, there's no sense in spending a #1 pick on a guy this year. One of the available veterans could be another short-term bridge to buy the Cardinals time to remain competitive while finding someone they like better in the draft (or developing a lower-round pick). Or, who knows, one of them could turn out to be the good enough to keep for the long term.
...dbs