Even in track events, as has been noted, races can be tactical. You'd be rewarding the runners who participate in rabbited races. Those runners frequently don't do as well in a championship race. By having a trials, you're putting them in an atmosphere most similar to the Olympics and saying if you medal, you go to the games.
I could see a system where someone who was top 3 in the world championships in the previous year gets an automatic spot, but otherwise, I think the trials is the most fair way to choose a team
The US style of having trials for everything seems so odd when you come for a country which simply has sent the three fastest athletes that beat the minimum qualifying standard. It puts so much additional strain on runners having to squeeze in an extra marathon. It seems entirely useless. Rank them after time and send the best ones.
Can someone explain me the American obsession with Olympic trials?