Once upon a time, you served your time as a copyholder and learned to read and write properly before you were allowed anywhere near the other side of the desk

When I got my first real job on a newspaper (1949) we had about 15 proofers. By the '60s the number had dwindled to half that.
I blame computers.
When they came in with spellcheck it knocked proof readers off the job. (Never mind that spellcheck will pass cellar when the writer should have written seller.)
By the late 1980s into early 1990s the paper I worked on had one proof reader and only the front page stories,the police report and the occasional list of Grand Jury indictments were proofread!
Standards crashing all around us!
Now, as for errors in *books ... Arrrrrrrrrrgh!