[dTal]

And why are the established parties doing this? Why is it in their interest to keep advancing terrible candidates?

I dunno. I kinda do think voters are the problem. Or at least a link in a chain of problems, the next link up being corporate controlled media.

[harha]

I'd say barriers to entry - being an established party gives you more revenue, supporters to do campaigning, influence, etc.

One place that tries to do it better in my opinion is Switzerland. It has a lot of controls to reduce the ability of politicians to act poorly and limits the power of higher levels (if something can be resolved well locally, there's no need to have a higher-level regulation). A lot of process is thought through and in place to enable direct voting on issues. Additionally, it has many levels to get engaged, which lowers the barriers to entry, by being able to have an impact on a local level.