Bill, have you ever ridden?
Even if you're going with the flow of traffic, wearing neon green, have your headlights on all the time (as is law in California) and liberally use the horn, you STILL get cut off because people just aren't looking. It's not so much size as it is shape; a motorcycle doesn't LOOK like a car. You run into the same issue with FAR less severity on a bicycle.
And drivers these days seem ALWAYS to be on the cell phone, even on Hwy 17 (I think that should be a legal test of insanity). It's inattention.
I had one instance in college, driving with traffic downhill on Hearst Ave. in Berkeley, where a driver very slowly changed lanes right into me without looking, didn't notice the horn, and didn't make any correction until my passenger gave him a hard thump on the trunk llid with her fist.
A few weeks driving a motorcycle is a great way to work up the defensive driving.
Now, I make a point to notice motorcycles. It isn't very hard; one just has to remember how to turn and change lanes like we all learned in high school. As in signal-mirror-overtheshoulder-go. It's amazing how few people actually do this.