Turnitin? They get the works from students/academics who submit works to turnitin system. By get, if the students/academics want to pass the course/check, some graders/reviewers require use of Turnitin. Compulsory courses tend to be big and graders use it as a tool to reduce grading time. I even saw a lecturer requirement to submit code in via Turnitin.

The system works well but some people do not appreciate their works being devalued and reused forcefully. In my last two years, I've attached a licence to my works that's uploaded. I suppose if I find my works used elsewhere with profit made from access to it, then they're infringing on the licence (CC Non-commercial).