I don't think it's hard to figure out at all. These journals have something people want, prestige.

Scientists are free to publish in whatever journal they want, including open source. They chose not to. Yes, you could argue it's not much of a choice since their tenure is dependent on publishing in these journals.

Start convincing the people who make the important decisions to stop looking for "Science" and "Cell" in CVs and the problem will solve itself.