I believe they have Facebook envy and now wants to keep every visitors they get on the site for as long as possible, just like Facebook. This is a departure away from their original philosophy in which their goal was to send users to the most relevant site for the user query as fast as possible.
I hope they haven't forgotten that the reason Yahoo lose out to Google was precisely because of this. Yahoo switched their vision from a search engine to a portal, and their product search engine start to suck.
This is dangerous. The best ad platform (which generates the most revenue) are those that are most efficient at sending traffic to advertiser's properties. Facebook main source of revenue comes from mobile app install ads which direct users to the app store for download, and page post ads, which sends traffic to advertiser's website.
A change in priority to hold users as long as possible on Google search isn't very tenable in the long term.