Emotively, closing the lines is unappealing. Politically, the withdrawal of rail services would promote an agenda that Holyrood/Westminster/wherever doesn't care about rural areas - especially if funds were used to improve services in cities.
Economically, the Far North would be better served at lower cost by buses. One of the better flows (Ullapool for the Stornoway ferry) has
never had a rail service, and the bus goes from Inverness rather the nearer stations at Garve or Dingwall. I expect something similar is the case for the West Highland.
Unfortunately, the suburbanisation and homogenisation of the rail network seems inevitable. It's a boring future, but it's probably a more effective one. Perhaps Fort William-Mallaig can be kept on as a heritage line for enthusiasts of such obsolete things as steam locomotives and wizarding schools.
I also find your argument that "everyone drives anyway" supremely unconvincing. I should imagine that there are many motorists in the far north who wouldn't relish the long slog down to Inverness, or even further by car.
It's actually quite the opposite: motorists in the far north are simply accustomed to the idea that once you've started the engine you've got several hours travel ahead of you. Once you've gone to Inverness the easy run down the A9 to Perth and then the Central Belt is no great hardship.
My wife and I are from the Highlands, and occasionally surprise our friends further south with our Highland conception of distance. It's much more similar to a North American concept of distance than to England or central Scotland. Trips we've done have included
- 120 miles each way to go to the cinema
- 55 miles each way late at night to pick someone up from a concert
- 325 miles one way, starting in the small hours of the morning, before attending an event all day and into the evening. Then the reverse (including all-day event) the next day.
Or you drive to Wick Airport and fly. It's not that long ago that you could fly Wick to Inverness - it was the only UK scheduled internal flight where both airports were (a) on the mainland and (b) in the same local authority.
Also I can imagine that there are many households who aren't multi-car households. Supposing Doris needs to visit Aunt Flo down South but her hubby needs the car for work. So many commentators on these forums seem to forget that just because people can drive, doesn't necessarily mean that they have access to a car all of the time.
Honestly, in that part of the world there aren't many households that have
fewer than one car per adult. It's impossible to rely on public transport, so everyone who travels needs access to some kind of vehicle, and really you want backup in case one of them breaks down.
Even if you don't have much money, a car is so essential in the Far North that people will make sacrifices to keep a total wreck running.
You cannot have someone working on their own for 3 hours with the public. Even in the highlands.
You can if they're a bus driver.