> actually operates 24-7

Good one. They routinely shut down lines and stations for hours/days at a time. The L got shut down between Bedford & 8th Ave for the entirety of Memorial Day weekend. Even when lines are running perfectly, at night they only run once every 30-60 minutes. To riders the changes feel arbitrary and are impossible to predict. I've been stuck dozens of times in random places because I tried to use the wrong line at the wrong time. The only real way to know there's a problem ahead is to have the privilege of riding that line on a regular basis and reading the signs they post. If you look around almost every station will have posters denoting some change that's ongoing or coming up.