Professors and researchers should start charging for time spent helping the closed journals at the very least. If you think your reviews are valuable, charge accordingly. You provide value to the publishing process and should capture that value. You are providing the service of "expertise". If you provided that service to a lawyer, you would earn several hundred dollars an hour. There's probably a business opportunit…
Professors are the producers and consumers of these journals. So, a group of your peers invests time reviewing your work and giving you helpful feedback, and you pay them back by reviewing other people's work. Basically, it's a zero sum game. So if everybody paid for the reviews they did and then got paid for doing reviews, a lot of money would change hands and everybody would end up with the same amount of money the…
The companies that publish the journals don't take a cut, they take the lion's share basically, paying a professor to review would work better in having them take a share of the pie.