 Part of the point is the pressure, actually. This setup shows not just who is the fittest that day, but it shows who can perform under pressure in a championship setting, you know, with all those eyeballs on them. It's also a bit of a logistical tactic, because so many people trying to make Olympic teams are currently college athletes in the US or Europe, so holding Olympic trials now lets them finish their college seasons in the late spring, early summer.