In those days, the people didn't have diddly. There were no recordings, no copyrights on sheet music, no way Beethoven had to make money as a musician other than public concerts and giving lessons. He might have been a rock star today, but he didn't have it that easy then.
Mozart died in debt and was buried in a pauper's grave.
In addition to this, Europe was ravaged by the Napoleonic wars and their aftermath during the early 1800's.