My guess is it's because the commute is really up to the employee. So if someone moves does the employer adjust their salary? What if I ride to work on my bike a few times a week (15 miles)?
Perhaps there could be some time stipend, so days may start a bit later and end sooner than 9-5.
Some companies do indeed do transport stipends for this reason. $100 a month for gas, maintaining a bike, bus/train ticket reimbursement, etc. Doesn't happen often and it doesn't replace the time you take, but it's not unheard of.
Time stipend would he interesting, but Idk if it'd really gain traction, especially with more white collar work offering full remote.
Perhaps there could be some time stipend, so days may start a bit later and end sooner than 9-5.