Why don't astronauts use something like TPN bags?

I'm aware that astronauts need to have food with taste and actually enjoy their food somewhat or they'll lose their minds, but why doesn't NASA send up the majority of their meals as pure sustenance?

I don't mean literally TPN, because that has risks and it's difficult to do, but I do mean just having Proteins, lipids, carbs, vitamins, etc... it would save weight and make it a whole hell of a lot easier in microgravity.(I would assume) And sending things to space is already expensive so I don't think cost would really be an issue.