Last weekend was beautiful and I went riding up my favorite twisty mountain. About halfway up, I came upon a pack of cruisers. As an observer, I was fascinated by how slow they were going.
When they came to a corner, they (at least the last two riders) stayed bolt upright like they were in an easy chair. They didn't pivot their head to keep the horizon level. I had to try it. After several corners of keeping my head in line with the bike, it felt like I was on a carnival ride. I almost got sick.
So it wasn't their bike's fault (I never saw anything scrape) they went slow, it was the rider's fault. Instead of being smooth, they were pretty jerky around corners. They were probably experts at cruising a straight highway, but didn't know how to take a curve. I bet most cruiser riders never take a riding class.