Because your life is measured in hours, not miles.

Also for the most flights the alternative is not driving or riding a train, but not travelling at all over that distance.

Examples: 1) unnecessary business trips ("that meeting could've been an email"); 2) long-range vacations ("let's travel somewhere local 1-2 hr by car instead of 3-6 hr by plane")

You can choose between time of the road trip to the place + road morts vs flight time + flight morts.