Why have these companies been so successful at curating prestigious journals?

I hate our academic publishing model. But I'm careful dismissing the journals as pure rent seekers. Their is a source to their staying power beyond merely habit.

However, I suspect much of the staying power is that organizing and executing on a top tier journal, or equivalently replacing it, is real work - and it is real work with no model for getting paid for or otherwise compensated for in an academic career.

There is also some value to being arms-length. A few top universities could gang together to pay for a flight of journals, but there would understandably be concerns about acceptance policies, etc.