He was their first choice and he preferred the Jets.
That isn't a big contract for a starting QB, though. If the Steelers really wanted him and thought he was the guy, they had the bandwidth to outbid the Jets.
There were some reports leading up to this that Fields wanted assurance from the Steelers that he would be the starter. The fact that that may have been a conversation, again, tells you what the Steelers thought about Fields.
It just seems like the Steelers didn't trust that Fields was the guy