Does sharpening fishing hooks really cause them to rust more easily?

Depends on the steel* the hooks are made of.

Hooks are heat treated to harden the steel then plated to protect the steel from corrosion. The plating is usually electroless nickel to help coat the point, electro nickel doesn’t cover the sharpe point.

When you sharpen a hook protected by nickel the sharpening process removes the plating exposing the bare steel. Steel corrodes exposed to some water with salt or acidic content.

Soft plastic loaded with salt or attractants with acidic chemicals both corrode bare steel.

*Hooks made from vanadium-chromium steel are more corrosion resistant.

Tom