I've many Udemy courses and my observation is this:
Most course creators do absolutely no video editing. Sure they slap in an intro but that's it.
So you'll get a lot of umms, & silence, waiting for the creator to gather their thoughts.
There's also a lot of filler content. So a 2 hour course might have 1.5 hours of history, reasons for the course, setting things up and 30 minutes of useful stuff.
So I watch most videos at 1.5x speed or more. I also download Udemy videos for offline view - therefore, Udemy doesn't know which courses I've left untouched, started, abandoned halfway or completed.