Speaking seriously, is it cultural?
Thinking to my own career, German colleagues and business partners have always been very professional and straight forward to deal with. Much like Japanese counterparts for instance.
From the football standpoint, I don't recall any players of theirs that I'd call out as prissy little punks. In fact, the last German player I distinctly remember having any sort of public say on his feelings was Sebastian Deisler. I recall him suffering from depression and something to the extent of not having the right attitude in the country to deal with it or appreciate it. Something like that.
Maybe it is just a big stereotype but that's my reasoning.
Nah, it's not a stereotype. As a german I had to deal with a few american businessmen (who were responsible for deals in the 6-7 digit range) and we talked about the differences in how business is done. Germans are indeed straight-forward and go right into the business talk and keep the small-talk for after.
A much more interesting was brought up by one, though. Mainly that germans often tend to not get the very most out of things. This does not mean that they want shitty deals, but rather that they understand the other side also wants to have a good deal out of it. You can also see it in german culture in terms of bargaining. Yes, there is a little bit of bargaining, but nothing ridiculous. When someones labour or product is - lets say- worth 1000 bucks, germans will not offer 500 bucks for it. They will maybe try to go at 800 and see, if they can get a little bit of a better deal, but not pushing it into ridiculous areas. Same seems to be part of the business culture. It is accepted that certain players are worth around X - and then the DoFs get together and bargain about where around that X, but none would get the idea to offer or demand Y when it's unreasonable.
Personal anecdote: In germany we have ebay.kleinanzeigen (formerly a different company that got bought by ebay) which is a bit like craigslist. Essentially people can offer products or labour on there. Often, but not exclusively used for second hand stuff. I like to use it quite a bit to get rid of unused items. If I then put an item in for 100 €, I very very seldom get offers that I would consider rude by germans. Sure, some ask me they are willing to pay 70-80 for it. But the ridiculous offers are usually from non-germans with stuff like "I buy for 30. Will get today". And that's quite common to the point I've seen plenty of sellers on kleinanzeigen even adding "I will not sell to non-germans anymore".
Another point is - as mentioned - the german DoF. Sure, the coach will have a say in transfer-signings, but generally there are two approaches to signings:
1. Scouting finds an still under the radar-player. Head-Scout + Coach + DoF discuss. DoF discusses the budget with the management. DoF approaches the player and club behind the scenes for some time, discusses the interest and opportunities and then puts out an offer (i.E. if I remember Dortmund was in contact with Dembele 2 years prior the signing). Usually that starts already within the time period of closed transferwindows and all we get to see is when the deal is almost done.
2. Coach discusses with Head-Scout & DoF what kind of player(s) are needed. Scouts look what they got / can find. Go back to Coach + DoF and same as above.
Key is, all of that usually happens inbetween transfer-windows. Essentially the DoFs role is way bigger in german football business. So once the transfer-window is open, the pathway to the signings - if the DoF did a good job - is already there and only the last bit of negotiation is to be done and then the trigger is pulled.
Obviously there are also negative examples such as Stuttgart, Schalke, Hamburg - who all should play a way bigger role with their possibilities. But for every Stuttgart or Hamburg there is a Freiburg, Mainz, Augsburg who do really good work with the little possibilities they have.
Furthermore another aspect that was talked about was the lack of star-players. Naturally the Bundesliga doesn't have as much money as the EPL. Thus there is no Ronaldo, Messi, Mpappe or whoever hype around. Add to it the fact that german football fans don't particular care about the players gossip and the football media operates very different.
And last but not least there seems to be a general gentlemans agreement in Germany to keep things under the radar for negotiations. Except for Bayerns approach sometimes. Other than that most negotiations are done behind the scenes and only become public when they are done or at the very least there are legit rumours during the endstages of these negotiations.