Because conservatives have been very successful at implementing laws and policies that specifically target people who are more likely to not vote conservative, to get them not to vote or make their vote inconsequential.

Conservatism is always a slide toward authoritarianism

https://www.sciencedirect.com/science/article/pii/S2352154620300401

https://morningconsult.com/2021/06/28/global-right-wing-authoritarian-test/