Google is a schizoid company. On the one side, we have engineers inventing tech like AMP, a search engine, and self-driving cars and generally making the world a better place.
On the other side, however, are the ad folks that actually generate all the revenue. They're responsible for pushing all the organic search results off of the search results page, allowing interstitial adverts on mobile sites, and generally making the experience of using Google' products and services worse.
According to Techcrunch, the latter got the upper hand today:
Google today announced a change to its AdSense policy that will remove a limitation previously in place that restricted certain kinds of ads “above the fold” – meaning, visible on a website without scrolling down the page. The company says that it will now allow its 300×250 medium rectangle ads to be implemented above the fold on the mobile web, without resulting in AdSense violations.
These ads take up a good amount of space on a small screen as it is, but at least until today you wouldn’t have to encounter them unless you were scrolling down the page while reading an article. Now Google is saying they can appear on the visible part of the page you see when you first click through to a mobile website. That doesn’t leave much room for content – like the headline, leading image or article text – especially on smaller-screened devices.
This will mean more screen real estate taken up by an ad and less content, so it's going to suck for users.
That said, I can understand why Google changed their policy. Like any business dependent on ad revenues, the only way to make more money is to charge more for ads, increase the userbase so you can show more ads, or find new places to display more ads.
Google has a financial incentive to make the user experience worse (Facebook operates under a similar incentive), and today their attention turned to mobile websites.
Existing mobile ads focused on a 320 x 80 ad unit, and it hardly pays anything at all. So if Google wants to make more money then they have to allow for bigger ads on mobile.
This policy change was inevitable, as were all the others.