In my current case, because my local public transport service is not the most convenient.
I live in a medium sized city were we only have bus service. We have many lines covering “almost” all the city, but each of the lines only has a relatively small number of buses available. This causes long delays between arrivals and makes combinations very difficult when needing to use more than one line. Waiting times of 40 minutes in the bus stops are not uncommon. By car, it takes me 15 minutes to go anywhere.
Another issue is with pricing: in our case buying individual tickets VS a monthly pass only makes sense when you do more than 40 trips every month. It literally costs me more to use the bus than to pay for gas.
In the past I lived in much bigger cities with underground service and plenty of buses available, and I barely used the car, and didn’t even considered the pricing.
jdh