I don't blame them for that. It seems to me (a very early beginner in learning Japanese) that a lot of languages have a formal way of expressing things, and informal shortcuts which native speakers use almost always in real life. But when you're just learning, you need to learn what "wa" does and what "watashi" means, and thus having "watashi wa" may help.
It's like in martial arts you learn kata first, though if you get to apply it later you don't do the same kata, you do something else - but to do it, you have to learn to do kata first.
It's like in martial arts you learn kata first, though if you get to apply it later you don't do the same kata, you do something else - but to do it, you have to learn to do kata first.