Because without the need to be profitable, you get gross incompetence, corruption, and waste. See: California HSR, BART expansion, NYC subway expansion.
The power of the market forces private businesses to offer quality service. A privately run subway would never allow drug addicts and thieves run rampant on the train like they're allowed to in NYC and the Bay.
Pro tip: if I feel scared for my life or property at any point during a transit, you've already lost against a car.
There's "unprofitable"*, safe, quality public transportation in hundreds of European towns and cities, suggesting the common cause of those issues is not the "lack of profit motive", it's uniquely American.
* Unprofitable meaning, they don't earn enough revenue to pay for the service to run. However, they do provide economic benefit to the area far in excess of their government subsidy.
But those deaths are 1) rational and 2) avoidable by defensive driving. By rational, I mean they make sense - drunk driving, unsafe driving, and speeding [1]. By contrast, you never know if someone on the subway is a mentally deranged person (frequently experience this on BART), a robber out to take your shit, or just someone who's being aggressive because they're trashy (also frequently experience this).
Per mile, cars make me feel the safest. And that's what matters for what I (and others) end up selecting for my form of transportation. Obviously, I'm probably never going to die on the subway due to a train crash. But I could be seriously hurt or my property taken from me - and it wouldn't show up in the stats as caused by the subway because it's just another crime that happened to occur there.
Have you really never been unsettled and felt unsafe due to mentally deranged people at night on BART/NYC subway?
The power of the market forces private businesses to offer quality service. A privately run subway would never allow drug addicts and thieves run rampant on the train like they're allowed to in NYC and the Bay.
Pro tip: if I feel scared for my life or property at any point during a transit, you've already lost against a car.