Case in point:
I had to take my extended family visiting us to Manhattan for 2 days last week. Total 6 adults. The cost of taking the LIRR and Subway would have been upwards of $180 (LIRR $120 + Subway $60) per day! Driving was much more affordable (and convenient) even with the expensive parking charges of $50 for 12 hrs of parking in prime locations.
Public transportation needs to become more affordable first. I would have happily taken the train if it was comparable in cost.