The scientific establishment made up of mainstream scientific institutions and those that run them.The individuals that run these institutions control many aspects of main stream science. This control gives them the ability to limit research and distribution of material they don’t like. The scientific establishment includes those who control publishing, employment, research grants, research facilities and education.
This is not some deep dark conspiratorial but just people protecting their power and world view but the result is the same. This actually happens to some degree in all fields of human endeavor such as science, religion, politics, business, and education. Those on the inside try to keep out those on the out side that disagree with those on the inside. It is a natural result of human nature.