On some level the problem is that the television landscape has changed, but the way the networks gather feedback/make money has stayed exactly the same.
We're living in a hundred-channel universe these days. The amount of choice available to a viewer at home today is staggering compared even to TNG's hey-day, let alone how things were at the time of TOS (when at best you had, what, three or four networks and that was it?). With so many other choices available to them, the viewers are not as fixed on any one concept or another as they used to be. They'll just go away and watch something else instead, and the show (which relies on advertising revenue -- no advertising, no show) suffers as a result.
The way the networks look at their viewers hasn't changed to reflect these modern times. They still look at advertising dollars and plain old ratings, just as they always have done, except they're doing it now in an era when such methods are almost outmoded. Indeed, with internet multimedia at our fingertips, we're not even limited to watching what the television broadcasters all want us to watch. We can programme our own viewing entertainment. You can no longer rely on the factor of 'if enough people watch this then we can sell more stuff and make money', because in this day and age you can never guarantee that enough people will watch anything. To be a success on modern television is harder than ever before.
On some level, I'd say that as long as this old fashioned way of thinking persists, then the television landscape is only going to get less and less, as it slowly eats itself to death.
At least in the realm of movies, a product has got a fighting chance of making it's money back. I think that Star Trek's future lies fairly and squarely at the box office, not in the living room.
