Habit - what they have learned to do. If they never heard those words, they'd not have them in their vocabulary to say when they are stressed out and anxious. I do think saying the words to relieve stress and getting a point across is better than self-harm, or screaming, and that's a good starting point - communication. But as I stated before - it can't be left as a habit if independence and employment are a goal for the future.
Is this directed at me? If it is, I'd like to respond that I am also a parent, and have raised two children (one the valedictorian of her class, the other salutatorian of her class) who have had to deal with anxiety and sensory and social issues. That's on top of working 16+ years with teenagers on the spectrum, along with other students with a myriad of other issues. I am the most requested staff member at our school, according to our principal and special education director. So I do feel like I know what I'm talking about. But I get where you are coming from. Of course each child is different, and what works for one does not always work for another. But doesn't everyone here share what works, etc? Why limit who can give input, share information, etc?