Interesting, the goal of the fastest runners must not be to finish highly, if it were, they would distribute themselves to the additional races so that they had a better chance of winning. Instead, the claim is that they each keep running in the same races as they did before so that the slower runners do not have lower finishing places. Wait, not that either since then those new low finishes at the new races would be slower.
The top runners will continue to go to the major races (New York, Chicago, Boston) because they can compete with the best runners in the world, there are appearance fees for elite runners, and they offer better exposure for athletes who depend on sponsorship dollars to make a living.
As for the US Marathon Championships, America's best marathoners usually skip that race (aside from when it serves as the Olympic Trials) because smaller, less prestigious marathons that pay less prize money are often chosen to serve as the US Championship. Why (relatively) smaller marathons? So that your US champion actually wins the race (like they would at the Twin Cities Marathon) instead of finishing somewhere in the top 5 (but not first) at New York.
So I can't speak for every runner, but for the vast majority placing will not be a major factor. I ran a half marathon recently and came in something like 600th - but that number is largely academic I was only really competing against the clock.
That race had several thousand entrance, of which maybe 3 had a realistic chance of winning and another 10 of placing. The things that attract people to races are more likely to be the location (either somewhere convenient or somewhere nice to run), timing (how does it fit in with training) and prestige of the race.
Interesting the prestige of the race means your position is likely to be much worse. But distance races, people don't ask where you came, they ask how quickly you ran.
I note that they don't look at the top 3 finishers of big races... because those times have been falling (like the US Nationals). https://en.wikipedia.org/wiki/USA_Marathon_Championships
An economist might say that was impossible (for competitive people to deny themselves a precious placing goal), I simply find that it's unlikely.