Because neither rights holders nor politicians want people to think about DRM and copyright too much.

If those laws/rights actually became campaign issues or were uniformly enforced, the whole thing would quickly collapse.

Due to the scale on which people ignore these laws this would result in having to fine/punish/demand damages from at least a third of the (US, or anywhere really) population. Think about how long those laws would survive if you did that.

Because political campaigns tend to be about the economy and other things of more immediate impact.

They tend to be about popular topics. Sometimes that overlaps with the categories you’ve described and sometimes it doesn’t.

because people don't vote based on that.

For whom would that be a larger issue than racial discrimination, economic inequality, COVID, gun rights, or abortion access?

Wouldn't it actually fall under the umbrella of economic inequality?

Because the RIAA donates to both parties?