This is kind of chicken-and-egg problem. Today most established journals with high impact factors (= prestigious) are non-open-access. Publishing in or being a reviewer of a high impact factor non-open-access journal looks much better in a resume of a scientist than publishing in non-prestigious open-access journal.

For an open-access journal to become prestigious it needs high quality contributions. But at the same time an author of some important discovery will more likely to publish it in some high prestigious non-open-access journal. Of course for tenured faculty members it is not such a big problem because they have a secured position. But for their apprentices not having high impact publications may become a problem in their future career. And while tenured adviser may force a postdoc to publish in an open-access journal most of them will not likely do this because they understand that this puts members of his/her lab in a bad position compared to competing scientists.

I think that well known scientists should make the first move here and to start publishing in open-access journals. Their work has a lot of traction and will not suffer from being published in some not-so-well-known open-access journal. On the other hand this will help open-access journals to start building reputation.