Because Vince McMahon is a genius business man. A lot of people were under the assumption that the company is going to shit because the ratings are down, but that's only a small fraction of the business. WWE's internal revenue streams (merchandise, WWE Network, house shows, etc) and their external revenue streams (USA TV deal, international TV deals, domestic and international licensing and marketing deals) provide a much greater measurement of company's stability than bad TV ratings and a bad product.
It's not that simple in the slightest.
First of all, 300 million TV money per year is not a "small fraction", it's a bit more than half their annual revenue.
In addition, success of other revenue streams depends on TV. Merchandise is sold because of exposure on TV. House show tickets are sold based on stories told on TV, based on wrestlers shown on TV. The major Network selling point of having the PPVs is based on TV shows hyping the PPVs.
Even if Raw moved to the Network completely, who would pay for it?
How much would those sponsoring and marketing deals be worth still if TV went to hell? Are you counting on a couple of Network sponsors?
TV is their bread and butter. Period. Without TV, WWE is an indy promotion run by an old guy who can't do anything else in life.
As far as stability on international TV deals is concerned, WWE now wasn't renewed twice within two years in Germany, a major market, because of piss poor numbers. And that after a long period of stability.
A business and ALL revenue streams are based on two things: the product and the consumer. If these two don't match, you're in trouble in the future. It's that simple. Especially if you put your self-righteous daughter in charge, and her husband, who never got anybody over beside himself through some revisionary history.