I am in now way arguing that those more and more terrible ads did not cause the surge in ad blocker usage, and what I said is not affected in any way by how many people are using ad blockers on NG.
Fact is, revenue per ad viewed has been crashing down for all type of ad.
A site like NG can either block their free access and force a subscribe (lose attention and name recognition), give it for free fully but remove incentive to subscribe (lose revenue), or change their ad type to more intrusive ad that pay more to compensate.
I'm sincerely open to discussion if you disagree, about what they could potentially do that isn't one of those three, but the revenue per ad viewed falling is not in their control, it's a global market trend since several years.
I understand that business needs may require a publication to lower their standards but it seems like they have dropped below where the floor should be. When I load the page, there's a giant Microsoft video at the top of the screen. Microsoft should be ashamed of that as well.
Only use "cleaner" ads ? It will pay less, ads don't pay much any more, you need the big, splashy, if-possible-exclusive-and-targeted ads to get money now.
Offer subscriptions ? They already do that, and they publish quality original content, so it's not the case of journal-X publishing the same press release as everyone and complaining that people don't subscribe.
At this point, they can only do two things with people who don't subscribe: block them from accessing content, thus losing lots of traffic and conversion possibilities, or show them intrusive ads, make a little money off of them, and hope a few subscribe.
One argument could be that "those ads are turning people off of subscribing and ultimately makes them lose money", but in every debate on this matter I have never seen it substantiated with actual numbers, and especially in the case of a household name like National Geographic I sincerely doubt it, at least not in any meaningful way.