Even when Rick was at Y! the push to move to linux was there. Rick had written most of the base libraries for freebsd originally (mdbm, ylock, ylock_kern, yfor, etc.), and tools like the package manager yinst and ysar, but being the great engineer he is, he ported them to linux and got the same or better performance. (In the yinst case he delegated the maintenance to a very capable engineer)
Note that Yahoo! was employing a few very bright freebsd kernel engineers but when the decision was announced that linux was the future many of them decided to leave. That made the path forward even clearer. It wasn't just a matter of integrating new acquisitions easier, and the fact that it was easier to hire people with linux experience than with freebsd experience. That was around 2008 IIRC. I left in 2010, and Rick less than a year later.
