The first time I saw minnows on the ground like that I was really annoyed and disgusted as well. In all honesty from what I have seen most people are pretty careful and try to keep all they collect, but there is always a bad apple, you know how that goes. Also you have to understand that those minnows are flipping all over the place when you net them, and it's easy to lose a few. Multiply that by lots of people and the minnows start adding up.

But mostly what happens is the infrequent moron who just doesn't care, if he misses the bucket and hits the ground he just nets more. It only takes one like that and you end up with minnows all over the place.