I don't know anything about you specifically, but your question is a good one. Why would somebody fake something? Turns out there are a lot of reasons. A big one is that people like to get attention (and everything that comes with attention), and sometimes they're willing to lie or falsify something to do it.
You asked! Like I said, I don't know you from the next person, but there are many reasons people are faking something like this.
Another is to discredit the real people it's happening to. For example, somebody who is very pro-vaxx might want to discredit those who don't agree with them, and might upload a fake video of the magnet trick. Then later, have it come out that they were lying, or just straight up admit it was fake. That would cause a lot of people to question the whole magnet story.
Just answering your question. Not saying you specifically would do anything like that, but it happens a lot.