IanCal's and a_bonobo's answers are correct, but to go further back along the line of causality: all of this is a holdover from the pre-internet days, when publ

IanCal's and a_bonobo's answers are correct, but to go further back along the line of causality: all of this is a holdover from the pre-internet days, when publication in paper journals was arguably the only or most efficient way to disseminate research results. Journal publishers were thus able to establish themselves as the gatekeepers in all the ways IanCal and a_bonobo described.