[vl]

I think there are two reasons for this:

a) It's extremely hard to make todo list app that accommodates all workflows that people want well. For example, RTM is not that well suited for GTD, but wouldn't you expect each of the most popular to-do list app to be well suited, for, you know, the most popular todo-ing method?

b) Sometimes manual steps are the point - rewriting list actually gives you time to review the items, so some people opt out for paper and such. I usually use RTM, but, for example, one-off packing lists I do on paper.