Because even though they make money, they are losing market share fast. Because of this, it is only a matter of time before they do actually lose money (unless of course, the NX can change that. People want to prevent that by making them third party.
Simply put, they suck as a platform holder. They only build with gimmicks or themselves in mind (ie no third party). Since they scare away mature third party games, and they themselves don't want to make them, they will always limit themselves to being a casual console (which shouldn't happen since a console should have games of all types). This, along with their old mindsets regarding online play and social interaction, makes them a pretty bad platform holder







