Borussia Dortmund has been doing this for years. They get the biggest criticism for this, but nothing changes. They see it as a business and think that selling players is more important than winning the championship. The criticism of football fans about Borussia Dortmund doesn't change the situation. They always sell their best players and try to find and train other players. They are actually very good at it.
Maybe this understanding will change and they will try to win the championship until the end and maintain their quality squad, but some clubs can't give up their habits easily.
Dortmund president has give the statement regarding why they had a habit always be sell their important players to other clubs this because Dortmund is not the club with strong financial such as Bayern Munich and with selling players to other clubs it can managed the balanced of financial club so that's why although Dortmund has received plenty of critism about their habit then they will always be doing that
Maybe if Dortmund didn't sell their players probably they can being an strong contender for race title for every season with Bayern Munich and imagined if Dortmund didn't sell Robert Lewandowski, Ilkay Gundogan, Erling Haaland, Jadon Sancho and Ousmane Dembele i think this team can be easily to gets Bundesliga trophy but unfurtunately Dortmund have to sell these players because they required money