I know that varies by region, but schoolchildren are generally taught cursive as a faster way to write. It already requires some memorisation with some glyphs being different from block letters. Why not make an additional step and completely replace it with shorthand, making writing an order of magnitude faster?
That was just the first result after a search. Its going to depend on who is trying to find historical documents, their goal, what they’re researching, who they’re researching, the time period they’re researching, the types of documents they’re researching.
For example, there are a lot of historical documents during the slavery era written by free african americans. The Library of Congress has a lot of it scanned and available as images, but not transcribed into digital text yet.