Because it was CCP that made that distinction. A while back. I can’t find the link, only people referencing it like myself:
If people make no effort to move to another area it is not harrassment.
If you have reasonable expectation of profit it is not harrassment.
https://forums-archive.eveonline.com/message/3544863/#post3544863
It may have started out as this post, but i do believe, like the others, that it was extended to anything where if you persistently target the same person with any activity despite attempts to get away, it can fall under harassment. But if the victim makes no attempt to get away, it is not thought of as harassment.