The drive to go multiplatform for these brands was always, you feel, going to happen. It was just a question of when. Microsoft's hardware failure has just accelerated the timeline for them, and their vast resources meant they could take the 'large publisher' approach.
The cost of games has increased exponentially, and these devices are being sold largely to the same people every generation. By owning the IP of large franchises, Microsoft are hedging their bets, ensuring that they will have a piece of the pie, regardless of what platforms emerge over the next 20+ years, whether they be handheld or even TVs. The console may be dead, but the brand has a future.
Nintendo and Sony have not been forced to have this conversation yet, but I wonder what their vision is.