The biggest reason people used to run ahead is because there were 8 people. The crowd reduced the responsibility of who was ruining it for the new players.

When there are 4 people, it's extremely common for people to wait, even for long cutscenes such as the one at the end of Aetherochemical Research Facility. They usually only pull a boss too early if the tank doesn't look at the party list and notice the cutscene, which is common in a dungeon just because dungeons make you turn your brain off.

I think the thrill played a part too. Speedrunning it was fun. And before it was ridiculous. How could you wait for a cutscene while fighting trash? At least now there is a balance so that you don't have cutscenes while fighting trash.