Seems to be a general concensus in these crush threads that the person crushing is typically new to dance...most cases it is a first instructor, first partner, etc. Probably the first time they are experiencing such close quarters with a stranger (in the beginning anyway), high emotional/physical charge of partner dancing, etc. Not to say it doesn't happen further along in one's dance "career", just seems by then we're either able to handle better or not posting about it since we've experienced before
Within the pool of instructors, the new dancer gravitates to the one that feels "right", unaware of all the powerful dynamics that such a simple thing touches upon. And suddenly...*crush*.
Painful or not, there's a lotta good stuff that gets brought to the surface during such times.