[Amokrane]

This assumes that you have access to the issues page. That's not always the case (when working as a contractor for instance). Also, tickets are not always filled properly, and often changes are not accompanied by a ticket. You get so many bonuses from writing good commit messages:

-> Overview of the latest changes without having to open additional links. Very handy for git bisects for instance.

-> Automatic generation of change logs.

-> It enforces changes that are purposeful and well scoped.

-> Knowledge stays with the Git repo. No data migration issues if you decide not to use GitHub anymore for instance...

-> And finally... it really just looks nice and professional. I would not take a project seriously if the Git log was just an aggregation of WIPs and Oopsies.