The reason is simple.
Teachers don't want to be talked at.
Just like our students, if you talk AT teachers, you're going to lose them as an audience. It is my opinion that teachers just want some guidance on WHAT to talk about, and then let them go.
Reel them back in, give them a chance to share, and then let them go again... for many different topics.
It's kind of like fishing. (Well, maybe not, but it sounded good when I used the word "reel").
You need to be patient as a presenter, be a good listener, allow your participants to talk, and you'll be fine.
That doesn't happen often, but it actually happened to me recently, and I really appreciated it! We had a chance to talk with others (this workshop happened to be about Math), and then we had some opportunities to work on our craft.
Believe me, this profession is hard enough, and if you go to a workshop and just sit for 5 or 6 hours... it's sometimes more tiring than actually teaching.
Thank you to those people that understand!
Keep up the great work, and ultimately, it will make us all better teachers.