In seriousness...some of it is that I may be unsure, especially when I mean something humorous, if it would be well received or elicit complaints.
Other times I delete stuff, I worry whether I am staying on topic. A little wandering is to be expected, but I know I can sometimes go off-topic.
On top of that, if it is a response to a question, unless it is something specifically stated in a game, I don't want to seem like I'm putting words in the creator's mouth.
Finally, I know I can sometimes ramble, and I don't want to take up space with my replies.