Borussia Dortmund has released one of its best players this season, Jude Bellingham. Yes once again we see them letting go of their prized players, and that is what we are used to seeing. I don't have a problem with this because Brussia Dortmund also benefit, but I regret it when they keep selling their valuable players continuously. The reason is that we know that it is currently difficult for them to break Bayern Munich's dominance, and when they got the big opportunity to break Bayern Munich's dominance, they failed to do so in the end.
Don't worry. It's dortmund's business. This team will be always doing it forever. Winning a trophy was just bonus but generating more and more money from selling developed players are very smart. 
Next season there is no guarantee that the same thing will happen as this season, because Bayern Munich will definitely evaluate how to navigate the coming season.
There will always be no guarantee for any seasons. The winner will remain unperdictable but bayern mostly winning the league. Dortmund will able to find the new players that have capability to replace the old one that was leaving from the club. You shall not feel worry about dortmund. This club knows what he has been doing by selling player.
they can get the new player that have same potential like the old one.
I know Dortmund is usually trying to seek younger talents and they sell the stars to top teams to earn money, but the fact about Dortmund is they have to also keep some players and earn achievement with the teams they have, in this season if Dortmund had a player like Haaland they could have a much higher chance in Bundesliga.
Also, I don't know if they spend the money they earn from selling these players because they don't buy other superstar players too.