The good ones snarf ideas from other good presenters when they see something useful.
A lot of bad ones imitate other presentations as the "minimum standard" because creating a good speech takes a LOT of work.
I'm also going to point out that a lot of tech speakers aren't native speakers of English. If you made me, a native English speaker, give a presentation in French or Chinese, I'm guaranteed to be a bad speaker.
Public speaking is a skill. It takes work and practice. Most tech folks have neither the time nor desire to do so.