Because their "yes" means a high degree of binding character, Germans expect a high amount of context information up front before entering into an agreement. First, it allows them to determine whether the agreement could have negative effects for them or their team.
Second, they want to fulfill their part of the agreement. Because little follow-up is expected during the time-span of the agreement, the better they understand the context, the better they can fulfill their part.
Because follow-up is frequent and because agreements can increase and decrease in priority, they can be entered into quickly without their overall context discussed in detail.
During an agreement the parties to it are in constant communication with each other. Full context information need not be communicated all at once, during the very first conversation.
Germans are surprised that Americans would ask them to enter into an agreement without having first provided the contextual information necessary to make a decision. They then experience Americans who become impatient with their questions.
Depending on the sensitivity of the agreement, a German might suspect that an attempt is being made to gain their "yes" without them fully knowing or understanding the potential effects. A German might become cautious, skeptical, even wary.
A German colleague requesting what can appear to be too much background information can give the impression of being overly conscientious, risk-averse, even mistrustful. An American would wonder, "if we have an agreement, why does my German colleague need so much information up front. Let's get started. We'll be in touch as we proceed."
Advice to Germans
Your American colleagues expect a high level of communication during the time span of an agreement. They do not need the whole story up front. Provide what is needed in order to get started. If and when they require additional information, you'll hear from them.
If an American provides you with too little context information in order for you to make a decision, kindly indicate this. Tell them that you simply are conscientious, that you want to get it right from the beginning.
Advice to Americans
Go into detail with your German colleague about the broader context of the agreement. Don't wait for the questions to come. Volunteer the information. And don't be surprised when German colleagues go into great detail with you.
They're neither long-winded nor pedantic. They simply want you to be fully informed so that you can make the proper decision, and if you agree, to execute to the best of your ability.