The last time I interacted with turnitin, I could easily see its shortcomings. That software is made to look for cheating and plagiarism. That works well for essays, but for math you're looking at a square peg - round hole problem. There are a lot of different ways to write a paragraph on an historical figure. There are only so many ways to solve a given practice math problem. It's easy to show that a history student copy / pasted from wikipedia, it's very difficult to show if a math student came up with the correct math answer on their own or googled it.
The proper way to asses learning in a math class is a live in-person test. Homework should be for the students to practice their learning, and if they choose to not learn while doing it that will be seen on the exam.