USATF bylaws require that USATF standards not be tougher than IAAF standards because the Ted Stevens Amateur Sports Act has been interpreted in such a way to mandate this.
The IAAF only has a marathon standard, no half marathon standard. So USATF could eliminate qualifying by the half if they wanted, but obviously that would be a bad idea. But can they make the half standard tougher? Yes, absolutely. Will that shrink the field? Maybe somewhat, but it's a pretty big qualifying window, some of the athletes who only had a half marathon standard would probably get the full marathon standard if they needed to.
The size of the field is not the issue. Legitimate safety concerns have been raised that affected the best athletes, not just the people at the back of the pack. Galen had to suck water from towels. Shalane had to get IV fluids after the race. This isn't simply a case of "the wannabes are whining about stupid shit that doesn't matter."
The safety of all participants should be a priority. Telling participants to only drop out near the start/finish line is insane. Telling athletes you'll add bottled water to the north station and then not doing it is unacceptable.
Max Siegel made a business decision. He made it really clear that having the marathon in LA made more financial sense for USATF and that is why he went against LDR's recommendation. He needs to hear from athletes and coaches about these aspects of the race, the things that he isn't thinking about because he's not a former marathoner, he's a guy whose job is to sell sponsorships.