Reason #1: too busy blogging/live-tweeting a show.
Reason #2: too envious of the wide, appreciative audience golden age TV shows enjoy.
(Ditto cat videos.)
Reason #3: you're sick of biding your own company.
Reason #4: you don't want to compete with the classics.
And the most compelling reason: you don't want your family reading your work.
More comics at Cat And Girl, Dinosaur Comics and Amazing Super Powers!