One of the biggest issues is that we force businesses and housing to have ridiculous amounts of free parking, which means that instead of dense areas where buildings can be next to each other we have a sea of asphalt with a building sprinkled here and there. In central areas these minimums amount to parking welfare for suburbanites.
People say to me "but it takes 90 minutes to go 15 miles on transit!!" - the problem isn't that transit should be faster, it's that you shouldn't have to go through 15 miles of primarily asphalt hellscape to get to basic amenities!
The core of Dublin is less than two miles across. I used to live in the middle of it and never missed a car. The core of San Diego.. well it's not really a core, and even then it's routine to have to travel several miles for basic errands, even if you live fairly close to downtown. A downtown that is prevernted from growing by parking minimums. Of course, if you ask a potential employer about transit access they look at you like you're from Mars (and, of course, choose to move on to a less hippie-ish applicant)