In the history of track and field and the Olympics, there have been many events where the level of performance in the US was so high that there could have been 10 athletes who were potential medallists. The US selection system developed around this high quality, because (unfortunately) it meant leaving potential medallists (winners even) off the team. This high level of performance gave rise to the situation of US Olympic Trials which were in many events just as competitive as the Olympics themselves. Qualifiers in these events knew they were going to be contenders for high placings at the Olympics. In this situation, "filling the team" is a very meaningful concept. However if you take an event where the US does not lead the world, such as the marathon currently, "filling the team" is a real luxury. I agree with the comment that getting the A standard should not even be an issue for an Olympic contender. You should realise that many countries in the world have their own selection standards which are much tougher than the A standard, typically being what it takes to get into the top ten. So why doesn't the USATF set 2 hr 10 as their standard, and forget about the principle of the Trials winner being automatically selected. As I said, I think a dedicated Trials meeting only makes sense when there is a surfeit of talent. If not, selection by committee is probably going to be better, especially if the committee can decide to select no one.
David Dallman