Why was my application for a one-year Thai Family Visa extension rejected?

Totally correct, you should have been denied your application

You can apply for a new extension in Chiang Mai when you have 45 days or less left on your current stamp

Your current entry stamp is valid until 24 Dec 2022 <-(89 days from the date you stamped in 26 Sept 2022)

45 days BEFORE the 24th of Dec is Nov 9th 😮

Today is Nov 2nd so you're 7 days early 😕

(Edited because I thought today was the 1st 😛 )