The Germany attacker was sold by Bayer to Liverpool for a record £125m over the summer.
Rolfes recalled: "At the club, we always keep an eye on what we can finance sustainably.
"When you have high revenues, it's not so easy to get players cheaply. With these sums, it's important that you as a club have guidelines to guide you. There are limits – both on transfer fees and on salaries."
Rolfes also said: "For Flo, we would have been willing to break out of this framework, especially since it probably wouldn't have been more than another year.
"We all know what Florian Wirtz meant to the team, the fans, the club, the region, and also to Bayer 04 internationally."
