Bag photo's are a small part and can be done internally and don't require the passengers present as is done with transit passengers.
As for matching ID in the US, I expect this is most likely airline policy rather than US security policy as they are domestic flights and if strict procedures were not in place anybody could fly under anybody's name. Saving them from been fined. This wouldn't be a problem for Int flights.
Think you are over analyzing self service desks a little to much, any technology can take automatic photo's if the US really want them taken at check in.
It isn't the technology that is the problem, it is the hard-soft interface, someone who occasionally travels vs a member of staff performing a task repeatedly. Taking pictures of the bags, as done in DUB, is really an automated process, though initiated by a member of the check-in staff. An automated bag acceptance system could just as easily do this. This is similar to how the T3 gates automatically take pictures of departing domestic passengers, which are then matched later. The issue is when the images get crossed. If my wife and I are travelling and I see her bag and she sees mine it isn't an issues since we know what each other's bag looks like. When I travel with colleagues I am not familiar with their bags. The issue is that this process can fail and when it does can cost the operators tens and hundreds of thousands in delays. It is not that these systems cannot be made to work. The key is that you deliver them in such a way as to work out the issues before you remove the viable alternatives. Unfortunately, I have found this often not to be the case.
US airlines safety and security policies are, in many cases, effectively the law. Failure to comply can in some cases be considered a criminal violation. This is because they have had the policy approved as a means of compliance to a portion of either the CFR or USC. Of course the airlines can propose an alternative means of compliance. This doesn't happen instantly, but as you say there is nothing, inherently, that prevents the use of automated or semi-automated systems, it just has to be properly proposed and rolled out.