You want to know what you're doing wrong...
Since this is art, this is "your perception through a medium." So you're not doing anything WRONG. But I will list a few reasons why what you are doing is perhaps not coming out as funny or as interesting as you want it to be:
1. Backgrounds should change, at least a little. Have you ever seen a movie or a sitcom that has just one background and doesn't even pan around it or zoom in on a character?
2. More sound, tastefully used, could help.
3. If the dialogue remains text-based, try to give the phrases more variety in terms of punctuation. The ellipses kinda wore me out.
4. Try to make the story more streamlined. It seemed like it was tripping from one weak gag to the next.