I'm not planning a bachelorette party as maid of honor
Why did you decide not to throw a party?
I just don't have the time and I wasn't asked to do it by the bride herself.
Even though the bride didn't specifically ask for it, it's commonly expected that the maid of honor will organize a 'surprise' bachelorette party for the bride to be. If you are truly unable to put something together, it is fine for you to decline the invitation to be maid of honor, and simply serve as a bridesmaid instead.
Asking to throw a party is too much for me.
If that's too much of you, then decline to be maid of honor.