Whilst there are cheaper options for car ownership, some costs happen regardless as to how many miles you travel a year. For instance if you do 1,000 or 10,000 miles a year you still need to service your car, you still need to pay VED, and so on.
All those costs increase the cost per mile the fewer miles that you do.
For instance if you almost totally use a car for travel to/from work and it costs you £2,500 a year to do so then over a standard working year that's £10/day. If your have an option to go by rail at £10/day then you're going to keep the car.
Now if you reduce the number of days you're in the office to 150 days and your costs fall to £2,250 (due to lower fuel costs) then the daily cost changes to £15/day, chances are that some people would opt to get rid of their car.
Now on the above is based on around previously doing 5,000 miles a year and that equates to 50p/mile (with the WFH option being 3,000 miles at 75p/mile), rarely does rail cost that much lower mile, so my guess for rail travel costs are probably fairly high.