I feel less sympathetic for many conservative states than this image would encourage, but even though gerrymandering doesn’t impact presidential elections directly it does impact state legislatures who then control the rules around presidential elections.
Every vote is counted, which is why there’s focus on voter suppression. If your legislature decides to make it harder to vote in liberal or more densely populated areas, voter turnout will naturally skew conservative. Same for shifting requirements to focus on criteria less often met by demographics that don’t support you, or changing the criteria for purging the voter registry and making it harder to register.