I ask myself this occasionally. You want the answer?
Because they're so freakin' easy to draw. Seriously. They're little cylinders. With wavy sticks for arms and legs, and knobbly balls (haha! I said 'balls') for feet and hands.
The last comic I made was way back in high school. It was called "Scuzzballs". You'd never have heard of it, unless you went to school with me. Then, only maybe. When Calvin and Hobbes creator, Bill Watterson retired his immensely popular strip, The Rockford Register Star held 'tryouts' for locals to send in their comics for publication.
To this day, I'm positive it was merely a publicity move, as another major syndicated comic eventually filled the space. Regardless, I was more than pleased that Scuzzballs even made an appearance. Just wish I knew what I did with the paper I saved from that day. Probably forgot it at my mom's house when I moved out later that year. Suck.
Anyway, the point: I admire artists, webcomickers, and cartoonists who can draw the same characters over and over, from different angles, situations, etc. I'm terrified of the prospect myself.