Earlier quoted context omitted.
Reading this doubly reinforces how good it is in Sweden where I live now. While trains and buses are notoriously delayed (somewhat frequently), I can look on a phone app and tell when the next one will arrive +- 1 minute. It’s no Switzerland or Japan, but it’s what a reasonably well run system looks like.
Truthfully, it's mostly a problem caused by the sheer population density. It's common for people to just head for the subway without knowing when the next train's arriving, which at off-hours can mean a 10-15+ minute wait for the next train. By which I mean: The concept of waiting around for an unknown amount of time for the next train isn't a huge deal. The problem is how miserable the whole experience becomes when…
That might seem like the obvious reason, but it's not the case at all. Read up on the NYC subway and its recent problems and their causes. Politicians use the growth in ridership as a scapegoat. There's more to the story than that. There's no physical/mathematical reason why a metro system of a bigger scale is precluded from running well.
Here's an article that offers a glimpse into various other angles and reasons:
https://www.villagevoice.com/2018/03/13/the-trains-are-slowe...