Because we elect garbage politicians who engage in wholesale bribery and are more interested in maintaining power than doing the job they were elected to do. We're getting exactly what we deserve, and honestly, I think that's too much.
The point of real democracy (versus what I call model/book democracy) is to extract useful value from fallible individuals while preventing them to do too much harm (like seizing too much power).
The better questions are then:
* Is it getting worse?
* Are politicians more preoccupied with their interests than in the past?
* Is it because it is easier now to manufacture misinformation?
* Is it because people vote for parties and not for individual politicians?
* Is having less focus on individual character an inevitable result of polarization of society?
* Would more truthful and unbiased news coverage help?
* Would more education on the principles of civic life help people make better voting decisions?
* Is technology causing general disease of attention deficit and focus problem on the scale of entire society causing it to make worse decisions overall?