Being called selfish over feeling hurt about being a bridesmaid?

Just curious as to why people seem to call others selfish if they are super hurt not being chosen as a bridal party member.
I am dealing with this hurt, but not involving any of the wedding couples family or friends.
I am also not going to bring this up with them at all.Posting and looking at posts tells me most people think the poster shouldn't have bad feelings and the wedding is not about them. Yes the wedding is for the couple, but how is me being sad at home affecting any aspect of the wedding? I can understand if I confronted the bride/groom or bugged them, then yes that is selfish.