>There only needs to not be a reason we need it to survive long enough to reproduce.

Humans had life expectancy even shorter than our fertility period until recently and they developed as social species hundreds of thousands years ago, for which living beyond fertility period is beneficial (grandparents were invented by evolution too).

> And bear in mind that most people don't have a problem surviving colds

That’s modern people with access to antibiotics etc.

> that was probably more true for much of our evolutionary history when we were living much more isolated lives, and not cohabiting with chickens and pigs

For much of our evolutionary history people were eating animals, getting viruses with them.

If you made it to fertility age your life expectancy was much longer.