They were going to make a sequel
From a Goldie Interview
Q: So why aren't the studios targeting older women?
A: Here's a good story. We did First Wives Club, and it netted around $250 million. It was a great success, but they didn't want to do a sequel. Diane [Keaton]—amazing, tenacious Diane—called me and said, "We've got to do this. We've got to make this happen." So she dug up a script that was rejected by them. I looked at it, and I thought that a lot of it was quite funny.