Spellcheck- meant to say don't...

Some foods just don't make sense 200 years after the war.
Stuff like
Squirrels
Iguanas
Salsbury steak

To name a few, surely they'd gave gone off/extinct?
I know it's just for gameplay but still, they could have put only stuff like honey, which lasts for 1000's of years or something...
Is there a plausible In game explanation or is it just gameplay?

Clearly squirrels and iguanas aren't extinct. Just because they aren't shown other the on sticks doesn't mean they have been wiped out.

Other pre-war foods last long because of "Science!" But even Three Dog in Fallout 3 mentions that it isn't that great to eat. All the other Fallout's besides Fallout 3 show that most people, stopped eating the pre-war stuff and farm and hunt new sources of food.