Plays during the Elizabethan era were big business! Money!
The more Plays a Theatre produced the bigger the audience and the greater the profit!
Plays were written and then performed as soon as possible - they were not printed until after they were performed
Shakespeare was just paid a one-off fee for the play - there were no Royalties!
There were no Copyright Laws to protect Shakespeare's work!
The actors used 'foul papers' or prompts from the Playwrights own copy of the play which were produced as a Quarto text (sometimes the Playwright would pay a scribe to produce a better copy of the play)
So rivals from other Theatre companies would copy the plays!
Rival members would attend plays to produce unauthorised copies of plays - notes were made and copied as quickly as possible
These would be taken to the rival theatre and another version of the Play would be produced!
These unauthorised and inferior text copies of William Shakespeare's plays were produced as Quarto Texts