Dortmund has been in the business of buying and selling of players to make profit for for a long time a team that is doing that has nothing to do with winning or trophies that's why you see their team finding it difficult to win trophies yet they don't get affected financially. They profit from the sells of players can equate to the amount they get in the trophies but it can't be compared to their ranking as a team in the league history.
Guirassy has not yet been sold because they may be planning to groom new set to players so that next season when he's sold the team will still have some good players I believe the team will be getting more profit if he keeps performing well next season.
Dortmund are focusing more on getting new players to perform for them whenever they sell the old ones that have done incredibly well and serve their purpose in the team. They are not the type that keeps players for a very long time without selling them off, they’re more concerned about the money they get from selling those players than the trophies they’ll get to win from keeping their best players. If Dortmund have been the type that nurtures their best players well and not rush into selling them, they will be a tough challenger to Bayern Munich every season and won’t find in easy winning the trophy back to back.
Guirassy is a great striker and it was for their own good they didn’t sell him, they’ll see his use more this season. Also, Dortmund owners are just into the business for the money making only, not also for the future prospects of the team to boast in the presence of others how many trophies they’re accumulated over the years of their existence. They should do well this season but I’m sure they’ll sell of their best players next season again when good offers come for them.