ABC is a communal obligation that, if, is not discharged by all, then every individual stands criminal.
Here what do we infer by not discharged by all?
Some have done it and some haven't.
None have done it.
Shouldn't we say: not discharged by any?
In short, if we say: It was not done by all. What does it mean?
No one did it.
Some did it and some didn't.