If the political spectrum runs from left to right, with a needle in the middle of whatever a given society finds acceptable, then major parties will align themselves immediately to either side around that needle.
This is how they can get as many votes as possible while differentiating from their opponents.
Your vote moves the needle further left.
Suppose 80% of the popular vote was blue. The republicans would be forced to chase that vote by moving their policies further left. The Dems would have to move even further left to differentiate themselves from the republicans.
Idiots on lemmy yelling you not to vote in order to teach your rep a lesson with your withdrawn support are naive to this well established political science.