Because if the situation was reversed and they were the clear cut leader, they would be singing from the rafters about unit sales. That's why they were more willing to talk about them last gen when the 360 was doing well. Sony did the same thing when PS3 and Vita sales underwhelmed, lumping "families" of consoles together and whatnot. I'm sure if the next Xbox (Two?) sells like hotcakes they'll start talking about it again, Play Anywhere be damned.
The narratives that these companies try and manufacture for PR points don't matter to me.
Have some time to kill? Read my shitty games blog. http://www.pixlbit.com/blogs/586/gigantor21