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.

Because they have compassion for those who suffer

if someone says im sorry for your loss you should say you should be!

yeah... i just don't know what else to say

It's a show of empathy...it's better than a kick in the pants