As someone who has worked with WSJ/NYT/LAT/Tribune on adtech in the past: that completely ad free subscription cost is significantly more expensive than you think.
Partially because those sponsored articles (native ads) pay a lot of money to be there.
Partially because they'd have to build and support a whole other version of the newspaper without ads, and if the subscriber count is low, that engineering/infrastructure cost isn't spread as much.
Those Google display ads do pretty much pay garbage though.
When we ran the numbers, it'd have to be a 3-5x increase in subscription cost to replace advertising completely. None of those newspapers think anyone would be willing to pay those costs.
The usual reason is people who are willing to pay to avoid ads are also the most valuable people for advertisers to advertise to. That decreases the value of their advertising business, which means they have to push the subscription prices up even further, which may make the business unviable. Especially because they have to compete with other businesses that will happily copy their content and put ads on it with no paywall.