Keep in mind, in math and other hard sciences it is not uncommon to cite 50 year old papers which are still highly relevant today (which is less common in biology). Such papers are often behind publisher paywalls since they predate arXiv. So closed access is very much a problem in these fields too.
indeed. it happens in life sciences too, but it's usually classic historic papers that everybody cites but nobody reads. In fact i have been completely unable to find some of the most cited works of e.g. Ramon y Cajal from the 1900s.
