I was curious, so I went the Wikipedia page, and it says[0]:
Not the least of these challenges was his unfamiliarity with the Cincinnati political scene, as he had never resided in or near the city, having grown up in the Cleveland area and attending college in central Ohio. The Post fired Watterson before his contract was up.
That passage cites an interview with Watterson[1] as its only source. The source material:
Watterson: I didn't hit the ground running. Cincinnati at that time was also beginning to realize it had major cartooning talent in Jim Borgman, at the city's other paper, and I didn't benefit from the comparison.
Christie: I'm not familiar...
Watterson: He's syndicated through King Features, and had been for a couple years by the time I arrived in Cincinnati. This is an odd story. Borgman graduated from Kenyon Collage the year before I went there, and it was his example that inspired me to pursue political cartooning. He had drawn cartoons at Kenyon, and landed his job at the Cincinnati Enquirer right after graduation. His footsteps seemed like good ones to follow, so I cultivated an interest in politics, and Borgman helped me a lot in learning how to construct an editorial cartoon. Neither of us dreamed I'd end up in the same town on the opposite paper. I don't know to what extent the comparison played a role in my editor's not liking my work, but I was very intimidated by working on a major city paper and I didn't feel free to experiment, really, or to travel down my own path. I very early caught on that the editor had something specific in mind that he was looking for, and I tried to accommodate him in order to get published. His idea was that he was going to publish only my very best work so that I wouldn't embarress the newspaper while I learned the ropes. As sound as that idea may be from the management standpoint, it was disastrous for me because I was only getting a couple cartoons a week printed. I would turn out rough idea after rough idea, and he would veto eighty percent of them. As a result I lost all my self-confidence, and his intervention was really unhealthy, i think, as far as letting me experiment and make mistakes, and become a stronger cartoonist for it. Obviously, if he wanted a more experienced cartoonist, he shouldn't have hired a kid just out of college. I pretty much prostituted myself for six months but I couldn't please him, so he sent me packing.
One should take content on Wikipedia with a grain of salt.
[0]: https://en.wikipedia.org/wiki/Bill_Watterson#Early_work
[1]: https://web.archive.org/web/20060212121427/http://home3.inet...