why do I need to enter the value of traditional IRAs on 12/31/2024?

If you have entered a Form 1099-R reporting a distribution from a Traditional IRA and your IRA is a mixture of pre-tax and after-tax money, then the total value of all of your Traditional IRAs is needed in order to calculate the amount of the distribution that is taxable.  

There are two different areas where TurboTax might ask for your year-end balance in traditional IRAs.  One is if you made an excess traditional IRA contribution and TurboTax needs to determine the excess contribution penalty which is less if your balance is less than the excess.

The second area is if you made a distribution from a traditional IRA and you have basis in nondeductible traditional IRA contributions.  In this case TurboTax needs to know the year-end balance because the year-end balance is needed to complete Form 8606 to calculate the nontaxable and taxable amounts of your distribution.