Hard tack, lifeboat crackers, military survival rations, are pretty far below normal fare for flavor and texture. This discouraged binging and helped conserve them for when you were really hungry.
OK... but I'm still going to go for food as nice as I can manage. There's a strong psychological component to survival. Morale matters. If all I have to eat is spam, I'm not sure I'll want to bother.
It may be a cultural thing. I think we in the UK have an antipathy towards spam that Americans may lack. It doesn't apply to other tinned foods, such as corned beef. (I have found tinned corned beef is better than the "fresh" corned beef sold in my local supermarkets.)
It's worth remembering the mantra, "Buy what you eat, eat what you buy". I stockpile tinned corned beef because I like it enough to eat it all before it expires. I have tried tinned salmon and similar, but because I don't really like fish it just sits on a shelf and never gets eaten.