@evan not only, nor even mainly due to XMPP, no.
My hypothesis is that they never cared about XMPP in the first place, but it was easy to deploy and gave them a nice PR boost from the techies that started promoting them with glee.
"No downside".
And then when enough users joined GTalk — partially brought in by the techies, partially calmed down by techies not warning them against it — they shut down XMPP s2s and moved away from the protocol eventually.