That's a very stretched definition of "full of".

Pre-pandemic I rode the subway to work every day. I'd see a handful of clearly unwell people on the train a week. I'd also see thousands of seemingly put-together people in that time. Is a milk jug full of milk and one jellybean full of jellybeans?

I cannot speak authoritatively for women, but my understanding is most of the danger comes from men. Not mentally unwell people, not the homeless, just regular men. Being unwell or desperate doesn't help, but it's not the only source of danger.

Furthermore, not everyone prefers personal vehicle transport. Maybe people prefer mass transit for a variety of reasons.