As everyone has continued to point out, shows get more expensive as they go on and there's no doubt that Paramount will pull the plug the moment they aren't turning as large a profit. And assuming the company shows interest in continuing the brand, that's why they create a newer "cheaper" show.
That's exactly why Voyager was created after The Next Generation concluded.
The TNG cast was tired and burned out from having done seven years. They wanted to get on with filming Generations.