The problem is, if you have 300,000 employees, it takes three or four years to make the change. By the time you finish, the “new” technology is obsolete.
I don't care whose technology you use, it needs to be refreshed on a 3 or 4 year cycle. Just start replacing Windows with Mac and in a few years you are switched over. You still have to refresh. Cycle is longer with Macs, but it is not infinite.