If it is a public job description why must it be https? Baseless criticism might tell more about yourself than about them.
Because you don't want a man in the middle modifying the job ad to say "must be 7 feet tall to apply"?
And finally because security should be the default unless there is a good reason to do it some other way. It's a bit like having an unpainted car because you're going to drive it in dry places where it won't rust... Unless there is a benefit to an unpainted car, most people take the painted car...