"what does "Scale" even mean here?"

I meant in context of the number of publishers that advertisers need to deal with to purchase impressions.

Cutting out the ad networks probably makes sense for Ster and NPO. I know nothing about Dutch media, but I'm guessing they're big enough to court large brands with big marketing budgets on their own.

[edit: The "Mass media in the Netherlands" Wikipedia page is bananas: https://en.wikipedia.org/wiki/Mass_media_in_the_Netherlands. I'm gathering advertising on NPO is regulated by a public body; the STER from the article.]