Businesses work people 40 hrs for a reason. If they only need people 30 hrs a week then they hire them in as part-timers.
What you refuse to address is the need in all kinds if weather to get from your home to the nearest bus stop or train station. And if after covering the ground necessary to get to those locations you then have to wait for the next bus or train. Sometimes you can time it right and only wait for a few minutes. Sometimes you miss the last bus and have to wait awhile. And sometimes the next bus or train is running behind and you have to wait longer. Then once you arrive you have to get from that location to your destination. If you're fortunate it's close. But it may take a 5 or 6 block walk. Been there, done that. Raining out? Take a cab! OK, how many cabs are needed to transport everyone off the train to their locations? It's not efficient. It's just an alternative for people who can't afford a car or for people who are commuting into a city who don't want to deal with traffic or pay for parking.