You're quite right, in that you can't answer for all Germans.
But you can answer for yourself.
You said in your original post "Let's see what money can do" as if the only possible reason he would leave Dortmund for City would be for money.
The better question is "Let's see how ambitious he is".
The reason no one leaves the Premier League for the Bundesliga is because it's a step down. It might not sit comfortably with you, but the German league is inferior to the English one.
City signed the best player in Germany last summer and he's not even the best player in our squad. The manager of the biggest team in Germany is quitting to come and manage a team whose stadium is "light years" behind. Are the best player and the best manager in Germany solely driven by money? If so, how did they end up in Germany in the first place, and why are they both jumping ship at the first opportunity?
The Premier League is the most competitive top league in Europe, as Jurgen Klopp is finding out. It's the most valuable sports league in the world. The most watched sports league in the world. Bigger than the NFL, bigger than the NBA, bigger than the Champions League. It is a global phenemenom. By contrast, the Bundesliga is one team regional league that no one outside of Germany really cares too much about.
The question shouldn't be "Why would anyone leave the Bundesliga for the Premier League" the question is "Why wouldn't they."