For example, I would much rather prefer to walk 30-40 minutes instead of taking a crowded, smelly metro for 20. I actually used to regularly walk 50 minutes to get home in the evening because I didn't want to deal with the transit.

There's also the fact that this is the time it takes when everything works well. Again, I take an automated line, which is fairly reliable.

But most of the other lines have "incidents" going quite often (more than once a week). In this case, if the delay isn't extreme (less than 30 minutes) people will just wait and stuff themselves in the even-more-crowded trains when they do show up. Or they'll try taking another line, adding to that train's usual crowd.

When there are too many people, trains usually have delays, because they have to deal with people literally not fitting in the train at the stops.

So even if you're OK with riding a train packed to the brim (say you ride from end to end, so you're guaranteed to have a seat and won't have to fight your way off the train), you still can't count on getting at your destination on time.