The Sharkticons appeared in 9 episodes of the G1 cartoon. It makes them a lot more popular than say Skids who appeared in only 2 episodes of the cartoon. Although Skids did have a prominent appearance in the G1 comics; the Sharkticons' appearance in the comics were all in alternate universes (mostly a future version of Earth-120185). And don't forget that the toy continuity is a thing too (in fact it's the prime continuity of G1).
Also, being a cheap army builder probably helps heaps. Gnaw, Wreck Gar and Scourge were the first army builder Transformers, but with all three being more expensive boxed figures, it just wasn't feasible for most kids to army build 'em. Gnaw wasn't even that interesting a toy to warrant splashing out a higher price point on. I remember skipping the toy in 1986 and later bought it loose complete in box in 1988 for $5. Gnaw is giving fans a chance to build an army of Transformers on the cheap.