Soooo… I’m going to take a stab at something that was addressed earlier in the thread by @JER and @Bensmom - who are both DEFINITELY much better informed than me on this topic. And hopefully one or both of them will jump in and correct me when I inevitably get part of the issue incorrect. Because IANAL, and am just a bumbling ammy owner 
But here we go. I think what I am understanding is that part of the risk of enforcing the code of conduct in the manner you are laying out is not just that the governing body has failed to enforce it that way in the past, and this might get sued.
There is a whole different risk that USEF is being careful about.
USEF is the national federation for an Olympic Sport, and as such, they have a monopoly over recognized showing in certain disciplines. There are also some specific laws that seem to speak to this status as an approved monopoly. But… part of the obligation is that they abide by their own by laws, and don’t act “corruptly.” If there are serious complaints to the USOPC about corruption and inequitable treatment on the part of USEF towards their membership… or major lawsuits about such an issue… they risk decertification as a national federation.
If they lost that status, then they would lose monopoly power. And… that could be a major issue. Hunter jumpers have been discussing this issue for a while. Eventing? Not so much. Plenty of people enjoy doing local and unrecognized events. But… these are mostly for lower levels. There is a very real risk to the entire sport world the national federation was decertified. I can’t speak to how that might play out, but I think that’s part of the consideration in the background. Sooooo… USEF is being exceptionally cautious and risk averse concerning how they are enforcing rules. And seems to have chosen to punting things to the FEI when they can for some time. But… that approach has also seemingly resulted in a lack of action on some high profile cases, which definitely causes people to wonder if the inaction is also possibly the result of corruption? And now there seems to be real risk from having gone too far in a different direction.
Anyway… I’m probably bungling how I am speaking to this particular issue. I don’t fully grasp it. But… I think that’s part of the puzzle when trying to grasp why USEF is or isn’t enforcing the code of conduct right now. Hopefully better informed people will speak up and correct whatever I got wrong here.