Respectfully, I disagree. A good commit message to me is something like:
[PRJ-123] Changed blah to foo
Blah didn't handle the wangle flange properly in some cases, foo is a better fit for customer requirements.
The "why" that justifies the change, is already contained in the JIRA ticket PRJ-123 and explains exactly what the customer requirement was that necessitated the change. It will almost certainly contain a lot of detail that isn't relevant to the commit message, because that isn't the place to be documenting customer requirements, and probably relates to a number of other tickets. Perhaps the code itself might have a comment explaining the code change, if it's a non-obvious implementation, but otherwise the ticket is the best place for that information.
Additionally, if a change requires multiple commits, you don't want to be repeating the justifications for the entire feature in every commit message. It's redundant. But the commits will all be tied together by the ticket reference in the commit message.
[PRJ-123] Changed blah to foo
Blah didn't handle the wangle flange properly in some cases, foo is a better fit for customer requirements.
The "why" that justifies the change, is already contained in the JIRA ticket PRJ-123 and explains exactly what the customer requirement was that necessitated the change. It will almost certainly contain a lot of detail that isn't relevant to the commit message, because that isn't the place to be documenting customer requirements, and probably relates to a number of other tickets. Perhaps the code itself might have a comment explaining the code change, if it's a non-obvious implementation, but otherwise the ticket is the best place for that information.
Additionally, if a change requires multiple commits, you don't want to be repeating the justifications for the entire feature in every commit message. It's redundant. But the commits will all be tied together by the ticket reference in the commit message.