I spent 19 years commuting on the MARC train between Baltimore and Washington. I drove into town exactly twice. One time was a one-way trip -- I left the office at noon and headed out for a long weekend trip. The other time I drove in to cart home the stuff from my office that I didn't throw out or give away. On both trips, despite the traffic jams on MD and DC 295, the trip was about 30 minutes faster than the door-to-door train trip. However, it was a lot more stressful, driving very crowded freeways at high speed in the dark. Getting out of town mid-day was OK, but downtown DC traffic is always a pain. The time I picked up my stuff, I stayed late and had dinner in town to try to beat the PM rush hour. It didn't help that much. The ride home was also crowded and the drive stressful, even after 7 PM. And, being February, it was dark.
I should also mention that the parking garage, while fairly convenient to my office, was about $25 a day. I didn't research what a monthly pass would be, but I'm sure it would be 100s of dollars. On the other hand, most of the larger employers in DC provide some sort of transit subsidy to their employees. This, I believe is mostly driven by the states of Maryland and Virginia (and DC) getting emissions offset credits under the Clean Air Act. It also probably part of the reason why the traffic isn't as bad as it could be.
So even though I could have gotten to work faster by driving, why should I put the wear and tear on my car and pay for all that gas and parking, especially when I get a subsidy for my monthly MARC pass and at least some of the Metro ride? I'm sure it's no different for people commuting into New York.