German prospect Reus chose to join the German champions over Bayern Munich and a whole host of other European clubs.
Badstuber said that the striker could have been a big hit at the Allianz Arena but has urged others to respect his decision.
"The player has made his decision and will have good reasons for it," said the German defender.
"We can only respect his decision.
"It's a shame though as he is a young German player and would have fitted in very well at Bayern."
Reus will join Dortmund from Borussia Monchengladbach at the end of the season for a fee of around £14.5m.