As much as Barcelona would love to welcome bids to cash in and try to balance their finances they wouldn't want to do that at the detriment of the teams quality and strength. Selling key players could see them return to the state they were in the previous season.
If Barcelona become careless with their team, they will loose the form that they have struggled to get all season. If Barcelona loose key players, they will return to their struggling phase where they struggle to win games. Key players in their team have mad it possible to get this far especially in their local league. Barcelona are just finding themselves, if they are not careful with transfer, they could scatter the team again and find themselves struggling onceore like they were even in their local league.