There are kids who struggle with these skills and they need extra help with them. Unfortunately some of these kids fail to master the skills even with many years of work. And that ends up being all that we focus on with them. Intervention is necessary. In theory a computer could do the necessary teaching but, most of the time, the sort of feedback offered by tutorials is not sophisticated enough.
Human intervention is generally important.
Students don't self-teach. Software can be used to help automate skills kids have already begun to learn. It can also be used to motivate kids to work on skills. As long as the computer activity isn't too routine or boring, this motivational element is very important. Well, it's definitely hard, especially to ask the right questions.