There's probably an element of selection bias here. Let's say, hypothetically, the media, writ large, decides "okay, these 20 politicians look dodgy, let's investigate them" in 2021.
It's plausible that something like this happens:
- For 10 of them, the dodginess doesn't ultimately check out.
- Five of them become aware that the media is onto them; either they give up, or their party cuts them loose. They don't run.
- Of those who run, one or two have their dodginess revealed _before_ the election. They lose (er, probably, maybe not, who knows, see Donald Trump!)
- Of the remainder, the media's been slow in digging up the dodginess, but one or two lose the election anyway.
- One actually wins, before the paper is ready to publish. (This guy)
Like, arguably, if the media was doing a perfect job here, you'd probably never hear about it at all; the dodgy politicians would never run, and "someone who _might_ have run for office but didn't is a fraud" is just not an interesting story; even if they bother to publish it won't get much circulation.
(There is another factor; when someone wins election that may prompt people to come forward with tales of their dodginess, too)