Revolutions stand or fall with public support. Voting is the most visible way to establish public sentiment. People like to quote that only a third of the US actually elected Trump, but do we have a clear idea of just how many oppose him, if so many voters apparently never expressed their opinion in any measurable way?
Doing nothing and complaining on the internet is useless. Doing something is scary. If you knew you had your community at your back, wouldn't you feel more confident to step up?
You're right that people need to know that voting won't be enough, but it's still important in order to communicate the public opinion that separates a revolution from a coup.