What is the intended purpose of it then?

Sometimes for different reasons: getting to know one another before the nikah, sometimes people were away for very long times away from home (wars back in the times of the Prophet for example), sometimes people do mutah and have a lawful relationship while saving to prepare the type of nikah ceremony they want. These are just some of the things I have seen. Mutah doesn’t have to be of a sexual nature it could be just so the intended couple can speak to each other and see each other freely.