If it's pasteurized, sealed in a can and stored at room temperature there's not much to make it go bad.

The molecules that make up living things (e.g. corn or Spam) are stable at the temperatures at which those things live. If you remove the bacteria that primarily breaks things down there's not going to be much change.

It's no different than a house with 200yo timbers.

Not quite food, but we found a bottle of Bailey's in my grandmother's basement that was maybe 20-30 years old. It had turned into Bailey's cheese.

When my grandfather passed, we found beer from the 50s and 60s (we guessed at the ages based on the designs -- it was stamped with local sports team memorabilia). We kept some of the Pittsburgh-sports team ones, in fact, and they're at my parents home on display with the rest of my fathers sports memorabilia. I also remember finding very old unopened soda bottles, though I am not sure what happened to those. Point being, I agree with you that it's probably not as rare as one might think on a first pass.