Because the real thing have male genitalia, and most of them have penis envy and phobia of pregnancy.
My second period (I started when I was 8-almost 9) I forgot to peel the back off of the maxi pad... so there was no sticky part on my panties. I was walking down the hall...after wearing it for 2 classes.. heading towards the playground, when I heard a bunch of kids laughing and doing stuff behind me... They were kicking my bloody maxipad around. I never admitted it was mine. That is the funniest thing I have heard in a long time, maybe my testoterone level is high cause im a bitch, damn.