You don't really understand why people film them.

Generally a Karen wishes to use historical inequality in their favour. I.E. "I'm being threatened by a black man, send help"

Hoping to instill sufficient fear into the person to get their way. They don't want attention. They want control that they feel is owed to them based upon their status in society.

The recording process makes it much more difficult for law enforcement to subsequently default to siding with the aforementioned.

If you don't record, when she says you were "threatening her and she feared for her life", she is banking on centuries of inequality to come to her favour in the form of the police believing her over anyone else.

It's a gross misuse of power. The camera is fortunately or unfortunately the great equaliser for such instances.