The problem is that consequences and discipline don't teach understanding of the impact of your actions on others. NT children don't learn this from consequences and discipline either. They learn it from natural development of empathy and ability to see things from another person's perspective, as well as their own experiences and the experiences from others which they learn about through being told or reading books or listening to stories in other ways e.g. through film/TV, along with the cognitive skill in being able to model scenarios and apply this first or second hand experience to the probable outcome of the action they are considering.
NT children do not stop being violent after toddlerhood solely because we have given them consequences and discipline. They stop being violent after toddlerhood largely because they have developed better self-control (in particular the ability to stop and think things through before acting) and because they have developed very easy, almost automatic access to much better ways of communicating and handling conflict, (such as talking), as well as the understanding discussed before and also because they pick up on social norms, modelling and context which tells them that violence is not acceptable in almost all contexts. (Part of this is consequences and discipline, but it is likely to be a very small part. Children learn MUCH more from social modelling and observing social interaction than they do from consequences).
ND children don't always pick up on social rules and norms automatically, and they may be slower to develop the other skills depending on their specific difficulties. However, many children with SEND needs who are violent do feel remorseful and regretful about their actions, because they are not necessarily being violent for selfish reasons, sometimes it is that they are losing control and having a stress response or losing access to all communication aside from the most basic which is violence.
ND children often find environments and expectations which are normal or easy for other children extremely difficult to cope with, which makes it harder for them to use the skills they have developed. On top of learning skills which are much harder for them to gain, they also have to learn to navigate a world which is not designed for them and manage their own triggers within those environments. This is often easier for adults, who have much more control over their environment. For example, as an adult you probably have jobs you would never ever apply for, and many people make that kind of decision based on the environment, and this is a completely normal thing to do. For example, I personally would never apply for a job which had me outside all day every day. I prefer to be inside most of the time. I would also find it very difficult to work in a noisy environment. Someone else might say they couldn't stand sitting still at a desk, and would prefer something where they can be more active. Someone else might say they could never work night shifts. We all have different things we find hard or especially dislike, and as an adult we get to avoid or minimise many of these.
Doing reflective work and learning their triggers would be excellent things to work on, but IME schools are not really equipped to work on this kind of thing and arguably it is not what they are really there for either. And even if children do find their triggers, if they are environmental they often have little power to change them and schools don't seem interested in (or may not have the freedom to) adapting to children in this way.