It stops companies from monopolising the market. Like what Adobe does with Photoshop.
That is only because:
1 - for what some people require of it it is the best tool for the job
2 - other people follow like sheep and use it because they are told that it is the best tool for the job, even though the jobs and skill levels are very different compared to those who need it
3 - no other manufacturer is willing to invest heavily in a competitor software package given the number of people who steal the Adobe software by using unlicensed copies reducing the market potential. The price that Adobe charges means they can still develop it from the income generated by the lawful users of the software.