Prepending a question with "I wonder" helps people stay in a collaborative mindset.

When you ask a question, it reads like a demand.

"How does this thing you brought up fit in [frame that I'm imposing on you]."

In an environment where people are freely sharing ideas of their own volition, asking a hard-to-answer or finicky question of them chills them wanting to share in the future.

Humans don't like falling through on commitments.

This is especially true when the commitments happen in view of an audience.

Someone asking you a question is an implied commitment to answer.

People feel an implicit obligation to answer a question, even a hard-to-answer, not-particularly-useful one.

However, when you prepend "I wonder…" to your question, you make it about you, not them.

The receiver can choose to answer it, if they find it valuable or generative.

That means if they do answer it, the answer will be of their own discretionary effort.

So it will be higher quality than if it were compelled.