Because no matter what happens in the 5 coming years, Dortmund will be below clubs like Manchester United, Bayern and RM in the mind of pretty much all players.
Although, they deserve more respect imo for their sportive success it would take some time for them to be on par with those European top clubs. You can see players like Mkhteriyan, an international recognised talent, rejecting EPL/Russia to play for Dortmund after they set Europe on fire this season.
I'm saying they'll lose players like Gundogan, Hummels and Reus too between now and two years and if they survive that too then they'll be able to be a international recognised club.