It's not something that constantly happens. There was a time last year when there was article upon article about that party going well over the 20% mark in polls, which you can compare to the 12.9% they got in the election.
Polls were clearly off about them before the election, but that's happen with parties before (FP in their biggest election to name one example), and while the party we're talking about isn't liked in popular media, or by other parties, they are of course also playing hard on the victim role because of this. We can just look at the various scandals around the environmental party in fairly recent times to see that media can certainly focus a lot on negative issues with parties on the left as well. You can only imagine what would happen in media if any of the established parties had scandals like the iron pipe incident (or frequent racism scandals in general), so the victim role is exaggerated.
And I didn't vote for any party I've mentioned either.