Everyone's said it already but:
- Public transport is widely awful and unreliable (and expensive - but I'll come to that).
- Convenience: would I rather be in my own space, with my own music, my own temperature control, my own choice when to travel, be able to get directly to the destination... or would I rather have to travel to a schedule, surrounded by other people and their noise/germs/children, have no control over the temperature, arrive near but probably not directly outside my venue, have to potentially change transport method halfway through my journey?
Fundamentally, lots of people will choose comfort over better for the environment.
(Yes, there are benefits of public transport over driving: not having to be in control/alert, etc. But largely I think driving provides better comfort and convenience)
- Cost: owning a car is undeniably expensive, especially as fuel prices go up. But with public transport, you pay for your journeys as needed and you have no 'extra' benefits other than your commute - with a car, you have that available to you at all times, for whatever you want, plus you can you use it for more than commuting, all within that cost. If I have a rail pass, I can't use it to rush over to my friend at 1am when she's really ill and needs someone to watch her baby. I can't use it to go and pick up a chest of drawers off Facebook marketplace. I can't use it to rush my cat to the vets. And so on. So you get much more for your money.
Plus, depending on how long your commute is/how wide your transport needs are, public transport is just as expensive.
A monthly rail pass for my commute would be £358.00 and I could only use it for that route. I own my car outright so spend £40 a month on insurance, there's no tax, and about £150 on fuel - a LOT less. Even if I were paying for my car monthly it'd still come out as less than that - with all of the extra convenience, usefulness and freedom that having a car brings without being tied to one specific route.
I don't love that I am reliant on my car, and we're moving closer to my work soon partly to cut my commute down as 50 miles is a bit much. But until there's really good public transport options with competitive pricing, I don't see how it makes sense financially for me to switch and if it doesn't make sense financially then I'll opt for the quicker, calmer, other-people-free option every time.