Because my mask is on my face and I do not take it off my face while in the water. Further, when I am going up the ladder I try to rinse my reg but often do not because I am bobbing up and down in the waves. As such, it all happens once I am back on the boat, that means snot clearing, peeing, etc. That said I do try to be considerate of others. Now if the fish would do the same and not drop trowel in front of me.
In Cayman if you take your mask off on the surface they send a helicopter rescue team. Best to get on board, conserve paper and discreetly send the sometimes bloody mess into the abyss. Besides, fish seem to like it. Now I know why I can't find a dive buddy. Cheers