If public transport were reliable, convenient and cost-effective then more people would use it. I tried getting the train to work for a bit. I had a change along the way. The first week, it was late 4 days out of 5, meaning that I got to my desk more than 30 minutes after my start time because I missed my connection. It also cost me more than the fuel my car would have used (at the time). An 80 % failure rate is not acceptable.
Now, if I go into town there is a very convenient bus route. However, if there is more than 1 person going then it is cheaper to drive in and pay for parking as long as you are there for less than 6 hours. Not to mention that the bus takes up to 35 minutes to get into town once I am on it (never mind getting to the stop early, waiting for the return bus etc, and half the time it doesn't turn up) and it taks a maximum of 15 minutes to drive. And this is a large town in the South East.
I grew up in Cornwall. There was one bus a day. It arrived in the nearest town at about 9.30, and returned at 13.00. Hardly suitable for commuting to work. If you needed to go to a different town, that bus was once a week. On a Saturday.
My mum still lives there and had to go for a "fit to work" assessment. She submitted her mileage and was told she could only claim public transport. She would have had to get the 9.30 bus, change along the way to another bus that only ran once a day but had already left by the time first bus got there. So overnight hotel needed (approx 4 miles from home). Get the bus the following day, go to appointment (luckily it was in the afternoon, otherwise another overnight stay required, now approx 15 miles from home). And then repeat for the return journey. They paid for the petrol.
The people who stipulate public transport for this kind of thing seem to have no comprehension that there isn't a bus every 5 minutes in every place in the UK. And actually, the buses where my Mum lives don't run any more at all - they were so unreliable (eg return bus wouldn't turn up, stranding everyone until the next day) no-one used them. So it was determined that the service wasn't required. Madness.
We simply don't have the infrastructure.