Here’s an example of train commuter fares in the Bay Area: https://www.caltrain.com/fares. Travel from San Mateo to San Francisco (3 zones, around 20 miles) is $200/month. That’s the discounted fare for a ticket. It doesn’t cover parking or travel to/from the train. If you need transportation to/from the train it can add another $50-$100 per month for fares, or more for parking fees and gas consumption for drivers.

And BART (a different rail system) is even more expensive.

That’s not negligible: that’s almost three hours of work for me to cover the cost (pre-tax). And I’m fairly well paid. Most engineers aren’t paid half as well. It’s a much bigger hit for them.