The entrenchment is due to perceived (and cultivated) prestige, less so about tangible benefits. Prestigious journals have good brand value, they spend money cultivating it and they extract earnings from it.
Researchers and administrators trade on journal brand value for career advancements. They benefit from a highly prestige-stratified journal catalog as a tool for differentiating themselves from their peers, it's much easier to justify a promotion based on 'X publications to prestigious journal A, B, C' than 'bunch of people in the community think this is a great result', especially to a non-expert.