Force and coercion can come from places outside of law or government decision. They can come from private actors, or, as in this particular case, from historically grown social structures.
As an academic, you are de facto forced to publish in certain journals that are considered to be important and of high quality. It is the collective status quo that does the forcing, as Robin_Message has already explained quite well.
(Coincidentally, most of my disagreement with most libertarians seems to come from the fact that they fail to understand or accept this relatively simple concept. If you implicitly assume that force and coercion can only ever come from the state, you're going to have a somewhat warped outlook on life.)
As an academic, you are de facto forced to publish in certain journals that are considered to be important and of high quality. It is the collective status quo that does the forcing, as Robin_Message has already explained quite well.
(Coincidentally, most of my disagreement with most libertarians seems to come from the fact that they fail to understand or accept this relatively simple concept. If you implicitly assume that force and coercion can only ever come from the state, you're going to have a somewhat warped outlook on life.)