Ah yes, a question as old as time itself. Or at least as old as September 1987.
I've actually written transcripts for the credits of the Snorks, and the credits for the first two seasons are very different from the last two. (I had an hour with nothing to do, and that's how I decided to spend it. What a party animal I am, huh?) If you watch the credits for the first two seasons, you'll see Brian Cummings, the voice of Dimmy. The last two seasons don't have him in the credits at all. What I think is that Brian left the show for some reason or another, and rather than find a replacement, H-B just decided to drop the character altogether.
Dimmy was the best character!!!!! A very sad day when Dimmy left the show. The episode where they went bird-fish watching was the best!!!
Another possibility is the writers changed and just didn't know what they were doing. Could've been that to make room for more Jojo and Corky, they got rid of Dimmy. If Dimmy had stayed, the show would've lasted another 10 years. Everybody identifies with Dimmy!
HI I DON"T KNOW WHY THEY WROTE DIMMY OFF BUT HE KIND OF CARRIED THE SHOW WITH HIS JOKES AND ADVENTUERS HE REALLY PUT SOME COMEDY IN THE SHOW MY FAVORITE EPISODES WITH HIM IN IT WAS TIME OUT FOR SISSY"S AND NEVER CRY WOLF FISH AND THE LITTLEST MERMAID
I don't think anyone will ever know why the writters wrote Dimmy off, but all I can say is that it was so stupid for them to do that! The only possible reason for why that occurred would have to be (like Ryan had stated) that Brian Cummings may have quit the show. I was also disappointed too cause to me Dimmy was such a cool character to be written out of the show. The last two seasons would have been better with him.
When I first read up on the show, I was indeed disappointed to learn that Dimmy wasn't in the last two seasons. While it was gracious of the animators to draw in cameo appearances of him, they simply weren't enough.
I think Brian Cummings left the show to work on another project, and the writers just didn't bother to find a replacement for him, so they decided to write him out completely. They also could've done it to make room for some of the other supporting characters such as Corky and Jojo. Who knows, really.