People are disgusted by the idea of eating insects for various reasons.
For some people, it's because they're invertebrates, which would also imply that lobster in undesirable.

But for many, I believe it is because they associate insects with decay and filth. When people see maggots, they don't see a rich protein source-
They see a squirming host of bone-white, flesh eating worms that violate the dead, and the unfortunate living, and may one day consume their own bodies.

When people see cockroaches, they think of rotting garbage, decaying feces, and other detritus.

People have experiences being bitten by insects, where they don't have experience with lobsters doing the same.

A great deal of work needs to be done influence people to see land arthropods as clean and edible, instead of as filthy eaters of carrion, feces, and waste.

Yeah, totally. You summed the thought behind perfectly.
Also the fact lobsters and shrimps are in the sea creates a disassociation from life on land. We don't live among those animals thus in people's heads it tends to go all to the seafood category.
The irony is that a lot of people consider shrimp a delicacy even though it could be consider the cockroach of the sea since it eats feces and detritus.