Why do we drive on a parkway and park on a driveway?

Why are there 10 weenies in a package, but only 8 weenie buns in a package?

Why do flammable and inflammable mean the same?

Why is there an "incorrigible" but not a "corrigible"? An "incognito" but not a "cognito"? An "incongruous" but not a "congruous"? An "indelible" but not a "delible"?