Recently, I have read some articles about the history of food pills. There is one article said that food pills "were seen as the next logical step in the evolution of food" in the age of space travel. But then it said food pills are not possible because "pills can never be made to contain sufficient caloric volume." (Visit http://www.bbc.com/future/story/20120221-food-pills-a-staple-of-sci-fi) Then here comes the question: If food pills cannot provide enough amount of caloric, then how can astronauts on space live on the food pills (or something similar like food powder that can be dissolved into water) ?
It's more expensive than regular food. Same reason we don't eat MREs. Because it costs money to package it the way it is. So it's much easier to just make a sandwich than eat dried meals.
It's not as good as what people eat in their houses. Seriously, it's designed to weigh as little as possible, so it's not going to be as good. Normal dinners taste way better, most of the time. For example, do you want a delicious, juicy, home cooked (or restaurant cooked) roast, or dried beef jerky?
The things that make space food "space food" are pretty much the same factors that make survival rations or military rations.
The food needs to be in a very compact form so that it can be easily transported. In the book "The Martian", NASA considers the options and builds a ship to bring Mark Watney several tons of protein cubes, rather than shipping steaks and potatoes. The mass and volume of the cubes is markedly less than regular food, and well as being better able to survive the rather rough handling of a space launch and a proposed airbag landing.
This bring the second point, the food must be capable of lasting for a long time in transit and storage. You're not going to step out of the airlock and stroll down to the supermarket to buy fresh groceries. The inside of even the largest spaceships currently are still about as big as a railway car, but subdivided into many smaller sections, so there isn't room for a big freezer full of steaks. Small, freeze dried packets of food can fit comfortably in a closet or packed in an corner out of the way. To do this to food requires a lot of processing, which is expensive and rather detrimental to the taste (US MRE's are routinely packaged with hot sauce to add flavour back to the food).
Finally, a consideration people generally don't think of is what happens after the astronaut eats. The food must have sufficient "bulk" to pass through the human gut, but you certainly don't want the space toilet to become clogged with waste. Getting a plumber to visit will be wildly expensive. Even urine needs to be considered, the diet has to be very controlled so astronauts don't get urinary tract problems, and if you are building a CLSS system, you would rather not be experimenting with exotic chemistry every time your system deals with an intake of urine. Astronaut food needs to be carefully blended to prevent long term problems with the astronaut's health, and also pass through the astronaut without causing issues for the plumbing as well.
Eating out every night at a fancy French restaurant will probably be cheaper than eating astronaut food, and certainly much tastier as well....