i don't understand why people say sorry after some disaster or bad news , sorry never helped me and why say that its not their fault ?

sor·ry
adjective
1.
feeling distress, especially through sympathy with someone else's misfortune.
2.
in a poor or pitiful state or condition.

I think most don’t know this is the definition, so maybe they don’t know why they say it, but it’s actually correct usage.