There is a lot of variation in how PhD studies work. In some places, you are just a faceless candidate applying to a department, which discourages you from cont

There is a lot of variation in how PhD studies work. In some places, you are just a faceless candidate applying to a department, which discourages you from contacting the faculty before you are admitted. In other places, you must convince a professor to supervise and fund you before you are even allowed to apply. Some universities require you (or your supervisor) pay tuition fees for a number of years before you can graduate, while others don't care what you do, as long as you can produce a thesis that meets their standards. You can jump from social sciences to STEM. Your formal admission can wait for a year or two after you actually started. Or you can move to another university and get a PhD in a few months, because the administrative requirements in the original one were too unreasonable. These things happen, because universities are independent organizations that like doing things their own way.