If, however, for-profit academic journals charge much more than it costs to produce them, I would expect to see for-profit startups competing with them.
Possible explanations for not seeing that:
There are for-profit startups competing with the big boys, but we just don’t know what they are, because of course they’re smaller and less visible than the big publishers
Startups get bought out by big publishers
Social barriers to entry like the impact factor issue you mention
Social barriers to entry amplified even further because startups are a bunch of entrepreneurs breaking into the field from outside, so they don’t have the same connections as scientists working in the field (less of a problem for big publishers because they can buy existing publishers)
Possible explanations for not seeing that:
There are for-profit startups competing with the big boys, but we just don’t know what they are, because of course they’re smaller and less visible than the big publishers
Startups get bought out by big publishers
Social barriers to entry like the impact factor issue you mention
Social barriers to entry amplified even further because startups are a bunch of entrepreneurs breaking into the field from outside, so they don’t have the same connections as scientists working in the field (less of a problem for big publishers because they can buy existing publishers)