Academia runs heavily on prestige. The journals are valuable because they are prestigious and it is more beneficial to an academic's career to publish in a more

Academia runs heavily on prestige. The journals are valuable because they are prestigious and it is more beneficial to an academic's career to publish in a more prestigious journal than a less prestigious one. Because the academics who publish in those journals get jobs at prestigious universities, every university needs to keep those journals in those libraries, because that's where all the highest profile researchers are publishing their articles. Anyone who wants to join that group also needs to compete to publish in those journals. It's a self-reinforcing cycle.