Yeah, I meant more like the money men who handle the day to day operations, bit of a hangover from following English football for so long. As to your question, I can easily turn it around and ask why wouldn't Dortmund turn down an opportunity to double their revenue gap over their nearest competitors? As I've mentioned, they've proved themselves highly adept at unearthing and improving emerging talent. Dortmund under Klopp appear to have almost perfected this, in fact it could be the reason why they didn't seem to be overly fussed about losing some of their best players in the last few seasons.
Because they are interested in steady growth and they can't hope to find a talent that will bring the same level of performance and character to the squad as Hummels (at least from the get go). Money that they can't spend wisely also does not help them and they are already looking at more than €100m extra from their new shares this fall.
Selling Hummels would also send a very bad signal to potential sponsors/signings and their squad.