Why Big Show?

Has there been any behind-the-scenes explanation for why Big Show has gotten this monster push after years of hanging around the mid-to-upper midcard? Were there simply no other top-tier faces available to feud with the Authority after Daniel Bryan's run ended (with Cena tied up with the WH title and Punk feuding with Heyman)? Does HHH just insist on feuding with someone his own age rather than newer talent? Why Big Show, now?

(And for that matter, given his age, how much longer can Show possibly keep going?)

The idea is that they're working backwards from Wrestlemania, with Big Show as Vince's avatar against whoever HHH has an avatar.  Why it has to be Big Show, I have no idea.