Gerrymandering would only change a state’s electoral college votes meaningfully in one or two states.

It’s more often an issue of:

1. Citizen becomes voter via “motor-votor” registration.
2. Later, state sends postcard asking to confirm voter’s address.
3. Voter sees postcard, looks like junkmail or fraudulent mail, discards without response.
4. State, not checking anything else, drops voter from roll.