There are many entities with vested interest to keep the data that supports their point of view, or their profit motive or their meal ticket alive. For example data collected meticulously by a underfunded biology professor about the allotropic speciation of the salamanders around the lake hole-in-the-mud would disappear in a jiffy. But flawed research supporting the efficacy of a patented clot busting drug would be perpetuated. Epidemiological studies showing the adverse side effects of the same drug would be hunted down and eradicated.
History is written by the winners. At least part of the data/research preservation is done people with vested interests preserving it selectively.