I think the plan was to trade a C for bullpen help but it didn't work out.
This was posted before, Rizzo gave an interview just after the signing in which he said that they initially wanted Wieters but thought the price was too high. Once his price came down, they jumped on him. I assume at the start of free agency Boras was seeking at least a 4 year deal probably for well north of $10 million a year.