As it turns out it doesn't actually cost that much on regular transit, there's an AIRPORT SURCHARGE because it's an "airport train".
No wonder Americans don't use public transit, even when the system exists it's ridiculously difficult and expensive to use.
Not required. SF does have an ordinance to cover some costs depending on the number of employees. But its not some nationwide law.
If you're a fancy tech bro in SF all your costs are covered, health/dental/vision/life insurance, commuting stipend or govt subsidized account you get to put pre-tax money in and the company might match, matching contributions for your retirement 401K. The techbro class doesn't care about the cost of BART, many of them take an UBER for 3-4x the BART faire and not bat and eye at the bill (or use the company UBER account for free). If you're just some random minimum wage worker, you'd be lucky to live within an hour or two commute of SF and afford housing.