what is the motivation for this new strategy by yahoo?

[Hali]

I can only guess that it has something to do with being able to track users. The more users with accounts at Yahoo, the more persons they can list as potential clients. Websites are bought and sold based on user traffic. If Yahoo can boast 3 million users, and FB 4 million users then its more of a competitive edge that can move back and forth, between several of the largest internet corporations.

As well with a captive list of so many users, they have a potential client base that they can advertise to, and tailor advertising to. They can also sell the lists of users, along with their demographics.