Well, because they love the heroine sooo much.
What do you know about love?!?! Can't you see how romantic it is to be stalked and then they answer with "I just can't let my bird go" or something like that.
I think it's an old and incomplete view of the shojo genre. And even so, it can be someone else fantasies.
And, some shojo publishing teams are sometimes very masculine, don't forget that the taitosha have a huge impact on the story and their characters.
That's why, go read Yumi Tamura's works (Yay Basara ! for example) or other good shojosei authors' works.
What do you know about love?!?! Can't you see how romantic it is to be stalked and then they answer with "I just can't let my bird go" or something like that.
/j