For the intents and purposes of this post, webcomics are not merely comics found online, because I find all of my comics/manga online. I define them more strictly as comics which start out as web-only publications. It is then self-evident why I refuse to include them in my regular reading habits.
Okay, the title of this post is why I don't follow webcomics, not why I don't read them, because I do. They're great. I find them to be the smartest and most entertaining illustration of concept for many articles, especially TVTropes main entries. But I never ever seek out the title, and here's why:
1, Very few of them are good. I don't expect to spend half-days sifting through the comic among the comics, the strip among the strips. I let the Internet do that for me. Still, I could have just subscribed to Penny Arcade or xkcd, which leads me to
2, I have a stringent idea of what kind of graphic storytelling I enjoy. Very often I try to broaden my horizons, but there's no reason why I would purposefully read something that has the worse chance of my enjoying it.
3, This is the most important reason, and it is related to 1, too. Webcomics are unprofessional. Now, the backing of a corporation has no inherent corollary with artistic values, but it implies that the comic has run through a pair of editorial hands that believe somewhere someone sometime would like the product. Oh webcomics can have plenty of peers, but peers are not effective editors. Editors know the pitfalls of the medium, have the obligation to advise against shark jumps and ego. Editors filter for me, then the Internet filters that output again.
A lemma, most of the creators are amateurs, and while the greatest mangaka must start out somewhere, I would prefer not to be that place.
4, All of my previous, serious attempts at reading webcomics were failures. I had a predisposition to like them, but I couldn't. I don't remember their names; I do recall that they were well-respected in manga communities (i.e., not the joke that is Power Axis Hetalia).
Because only on the Internet this disclaimer is necessary: I am not advocating against webcomic. On the contrary, please continue what you're doing, please provide a supportive community for these artists, please grow and thrive and smack me in the face with my ignorance. I would love nothing more