Because an inexperienced Prestashop user, when an error pops up at him, is afraid to do anything and will not change the file to FTP. The more experienced will do it, but will not give the entire error record, but only the header, or only part of it.
If the error is 500, the debug log may not be displayed at all.
And besides, no error may appear at all, where the name of the module will be written.