I am not sure that the Bayer Leverkusen sports directors and management are unaware how the situation might be. Perhaps they just wanted to make some money out of the players they have.
Nowadays football is not about winning. The business side is more important. I think winning is now a second choice. I think every fan wants to win but sometimes they don't think about how the club can turn around the finances and make a profit so that the club can survive for a long time. So it seems Leverkusenin is copying Dortmund style of doing smart business by selling players and bringing in new young talent.
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Why not keep to the balance by making sure to give the fans what they want while you're chasing on the profit for the maintenance of the club's life? Every club fan wants some achievement from his club to brag with when they talk about their club. It's nothing close to what Borussia Dortmund have been doing if that's what you think that Leverkusen are imbibing. Dortmund makes for a ready replacement from their academy immediately after selling their key players but this isn't what we see with Leverkusen. Lastly, how has Dortmund fared since they have been doing this? Rather the club has lost its top flight place in the league.