The simple answer as to why the Network is under performing is the product is not very good right now. That should be what gets Vince and others to take notice and improve, as it's directly effecting the bottom dollar. Unfortunately, at least for the time being, I'm guessing Vince just thinks more promotion or more Cena will drive the subscriptions.
It wasn't just the WCW competition that made WWF go all out during the Attitude Era. It was the threat of going out of business. If the Network continues to hover around 750k subscribers, they will have to do something about it or they'll go out of business. Either raise Network prices (which would surely backfire and cause a ton of people to not renew), cancel the Network altogether and return to a PPV model (would be a shame and I'm not sure there's any going back now. They've alienated a lot of PPV distributors, plus Vince would have to admit he was wrong), OR they could actually improve the product. Give people a reason to want to see MORE wrestling. With 5 hours of WWE TV a week, plus 2 hours of TNA, that'll be a difficult task.
*edit* According to this:
http://www.sescoops.com/details-wwe-tv- ... breakdown/" onclick="window.open(this.href);return false; the average WWE viewer is 41.4 years old. Viewership is 19 percent under the age of 17, 22 percent between 18 and 34, 22 percent between 35 and 49 and 37 percent over the age of 50. Yet, the product is very clearly geared toward children. They have the right demographic for the Network (people with disposable income) yet they can't reach 1 million subscribers. Maybe if they catered to their average viewer instead of that 19 percent under the age of 17, they'd have better results.
Damn metric system
