Illicit Copying is a form of theft which damages composers and publishers. It discourages composers, who may be forced to look for other ways of earning a living. It deters publishers from investing in new writing talent and the production of printed music and it denies them information about the use of music which would guide further investment decisions. A publisher may allow a work to go out of print believing that there is a lack of demand for that particular work when the opposite may in fact be true.
Source: Music Publishers Association (https://mpaonline.org.uk/)