Many people still don't understand the tactics used by some clubs like Dortmund and Arsenal at some point. It is like a farm to detect and to form talented players then sell them for a nice reward. Haaland was the best example, no one thought that Dortmund continued to win without him but they did win many times without having Haaland in the club.
What you say is very logical and also very reasonable because I personally also wonder why some people don't understand the tactics and business that is run by each team in terms of buying and selling players like Dortmund does. Even though it is very clear that there are other things that the team gets when they sell the best players like Haaland's example and on the other hand Dortmund themselves are also very aware that they can still compete in the Bundesliga even though they have sold the best players because they can still make other players the best to keep themselves strong in the competition.