Many reasons for unsubbing, just coming from my point of view.
The art drew me in, but I didn't have a feel for the story until more pages were posted.
The concept rocked, so I subbed, then found out that not only did the writer not have the concept down, but the comic was not even the concept advertised.
I actually liked the comic, but the creator wound up doing something that I found dishonourable and unethical.
I was enjoying the comic, but the creator started shilling hard, and berating people for not clicking on the ads. Seems click-throughs drive up the amount you can get from Google.
The writer did enough cliches in a row that I just could not take it anymore.
All of those are reasons I have unsubbed. I don't usually get that specific, but those are all general enough that I feel safe posting them. If I sub to your comic, you are under no obligation to sub to mine. Mine is an alternate history super-powered industrial espionage tale. That is such a niche market that I figure it will be a year before I get 500 fans. If you draw stick figure gaming commentary, and I subscribe because I like your sense of timing and snark, I'm not expecting you to even look at my comic, unless you're that odd person wondering where this story has been all of your life. It's just not reasonable.
However, that is your position, and it's not harming anyone, so go for it.
Now, anyone that I notice in the forums, and that includes people I interact with, I go check out their comic so there's that sense of community. Of course, these days, you are not even going to notice if I subscribe or unsubscribe, since I do all of that on Comic Rocket. Easier and more convenient.
Eagle
(And please, if someone unsubs me, please tell me why, I need the feedback)