Publications in peer-reviewed journals are how a career in science is built. It's impossible to measure the productivity of a scientist. What is done, is that one looks at their publications. How many publications do they have? How often are they cited? What is the quality of the journal?

This creates very bad incentives, leading to things like publication bias. It also means that you must publish in prestigious journals. You don't have a choice but to accept their terms. Libraries don't have a choice but to stock these journals. It's a straight-forward monopoly racket. These publishers make fantastical profits.

All that money can be used for PR campaigns and lobbying to keep the good times rolling.