The phrase 'bachelorette' is, as far as I can tell, the penis envy of the linguistic world. Bachelor parties reflect a truth that feminists find uncomfortable, namely that an unmarried man is just as likely viewed as a someone with options rather than someone that's been passed over by the dating market. That's why bachelor parties exist - men are spontaneously mourning the loss of a certain freedom of action.
Moreover, the world was not lacking in a term to describe unmarried women. The term is 'spinster', and unlike 'bachelorette', it doesn't come up as a spelling error when I type it in blogger.
So why don't we have 'spinster parties'? Simple. The connotations of the phrase 'spinster' reflect another truth that feminists find uncomfortable, namely that unmarried women past a certain age are generally not viewed as having lots of options, but as people that have been passed over. Don't shoot the messenger, but that's just how it is.
Bachelor parties are usually quixotic, last-hurrah type affairs, where the groom-to-be is sadly bidding farewell to certain things he enjoyed, while his bachelor friends revel in the fact that they still get to do them. "Bachelorette" parties (or 'spinster parties', as I like to call them), on the other hand, have the opposite dynamic - the bride is triumphal, having finally gotten him to 'put a ring on it', while the other spinsters are trying to be happy for the bride's success. Whether this latter part always happens or not I do not know (having never been), but I would be surprised if there weren't a reasonable number of attendees who were merely putting on a brave face.
And that's where "bachelorette parties" come in. It's not only a linguistic sleight-of-hand, but a serious attempt to ape the demeanour of the bachelor party - friends celebrating their freedom to drink and flirt and sleep with random guys, a precious freedom that the bride is about to lose. Nobody is fooled by this charade of course. And in the scheme of life, the bride is least fooled of all. She's got the man she wanted.
Fact is, no guests want to turn up to a 'spinster party' - who wants to be reminded that they're on the path to living alone, while their friends experience relationship success? Bachelorette parties are an attempt to paper over the truth of the dating market. And while I can support that, the phrase is so comically ridiculous I can't help but laugh. It's a dark kind of comedy though, with the tragedy side barely concealed.
Bachelor Party
Guests --><--Host
"Bachelorette" Party
Host --><--Guests