Dortmund are currently looking for a winger. Gnabry and Neymar have been entered as most recent rumours on Transfermarkt. Gnabry is a realistic rumour maybe but I don't think the same about Neymar. Because his salary demand would be huge and he is already making more than 50 million euros per year. Dortmund are paying Haller the biggest amount of salary now which is 11 million euros per year. I don't think Dortmund are interested in any experienced world star transfer now.
Dortmund is a typical club that buys players who are more affordable and they will try to improve the quality of these players for the better. Neymar is not the type of player that is expected to come to Dortmund and they are not going to waste a lot of money to sign him, let alone talk about the exorbitant salary that Dortmund has to pay every week. Gnabry would be much more affordable for Dortmund and I see a bigger chance Gnabry than with Neymar and if the rumors are true.
Because they don't have the aim of building a squad whose quality is nearly the same as Bayern Munich in the first place.
Dortmund is known as one of the clubs that can always produce great talents and they will sell them to other clubs when the players have developed rapidly, that is the business that Dortmund runs and they have never thought of building a squad like Bayern Munich.