Now the shareholders and wall street analysts are not going to get antsy yet about a beta not being active and progress not being made to release the expansion -- but they will start to if something doesn't eventually happen. Blizzard's one job as a publicly traded company is to make its investors money. They do that by releasing innovative and hugely popular games. A major part of that releasing is producing a beta test and generating press/publicity for the game and the company. So without the beta... well, eventually questions are going to get asked. The kind of questions a company doesn't want asked.
Second, the beta itself is going to compete for attention with Elder Scrolls Online, which releases April 4th. Make no mistake, the MMO market is competitive, and Blizzard knows how to play the game. There's always been a lot of scuttlebutt about how such and such a game is coming out soon and Blizzard is going to play dirty and release a new game around then. I don't buy that people like Rob Pardo are sitting behind their desk tapping their fingers Mr. Burns-style. But they certainly do recognize that there is a good reason to start to talk about the game now rather than when another AAA title makes it debut. Why force the larger community to pick between two games when a simple calendar move could allow everyone to have both? Blizzard is full of insanely good gamers too, they're going to be playing ESO, they get it. Co-exist.
Finally, and perhaps most importantly, is what the lack of beta is doing to the community's mood. Yes, much of the whining (for lack of a better word) about not having a piece of test software is only out of love for the game. But when you combine that negativity on a large scale, that want of new information, the need to see first hand what the future of the world we all play in will look like, it becomes an issue. Blizzard has dealt with some major community problems in the past, and they've responded, it seems, by becoming more and more transparent and accessible. You can reach any of the designers over Twitter, the forums are still read and are an active place of engagement between fellow community members, and the CMs are out and about more than any other company I know of. They're ready to handle the negativity associated with lack of info, but it's also a good idea to cut the problem off before it reaches a boiling point.
I'm fully aware that I contradicted myself in that last paragraph, and you can now take this post as just a bunch of whining about not having a beta. But I'm hopeful that I've laid out there's more to needing the next version of WoW than just my desire to see my characters at level 100. The shareholders need it, the market demands it, and the community sentiment requires it.