Estimated taxes and $7500 tax credit for electric car

The $7500 tax credit on my 2023 return brought my total tax down to $2182. Turbo Tax said my estimated tax for 4/15/2024 was 1/4 of that or $546 so I paid that. In September for some reason I can't remember I figured out that my estimated tax each quarter should be $1300 so I paid that for the next 3 quarters but did not pay the amount needed to correct for not paying enough in June. Now the IRS has sent me a bill for that difference. My question is WHY was $1300 the correct amount. I am not a high earner so my estimated tax should be 100% of my previous years tax.