My experience with PubMed is that I almost always only get the abstract and a link to buy the article from the publisher. Sometimes I get a link for the free f

My experience with PubMed is that I almost always only get the abstract and a link to buy the article from the publisher. Sometimes I get a link for the free full text article, but this is a strong minority. Is this because so many of the listed articles are not funded by the NIH?