The only player they sold to Bayern was Hummels. Götze had a release clause and Lewandowski left on a free after they refused to sell him to Bayern and kept him against his will, opting against the money (and contrary to what was expected he performed well after a few weeks of sulking).
Hummels to Bayern was pretty much a done deal in May, so they had an entire summer to plan without him. That's the major difference. Dembele was key in BVB finishing third and winning the cup last season and he is key in their planning for next season. Had all this started in June or early July they probably would have sold much more easily, but now they'd let go one of their most important players one week befoee the league starts.
Reus won't return before months into the season, Mor just left, Schürle is Schürle and if Pulisic picks up an injury they're pretty much screwed. So should Dembele leave they'd need a great replacement which becomes increasingly difficult the later it gets. That's why they're highballing. Not because they're greedy as such, but because they don't want to sell. So with that sum either they fend off interest or let Barça bleed as compensation for the inconvenience this transfer causes them.
For me, the guilty one here is Neymar. Without his stupid week-long silence we wouldn't be in this position.
