The one thing about TVP that most meat cannot do is be shelf stable for years. The flavored TVP's work so well due to that and being very light. They do not require long rehydration times and come back to life at high altitude. It is also considerably cheaper than using freeze dried meat - which, yes, can spoil if left exposed to humidity in air and not kept tightly sealed.

It also contains fiber, something meat doesn't have (which is why if one has never had it before, start with small portions!)