The majority of university research depends on external funding. In order to get funding, you as many published papers in high ranking journals.

You get zero credit for self-published papers, or papers in non-ranked journals.

So a researchers will always look after the highest ranked journal that is likely to publish a particular result. Issues of copyright get no regard and accessibility gets very little. Copyright ownership won't get you funding. Accessibility might get you more citations (which also affects ranking), but most citations come from other University researchers, who have access anyway through their libraries.