that's not exactly how depreciation is calculated. it's the business mileage each year times the portion of the standard mileage deduction that is depreciation as provided for in PUB 463 page 24.
can't answer why TT doesn't track this but various pro software I have used over numerous years doesn't track it either.
https://whttps://www.irs.gov/pub/irs-pdf/p463.pdfww.irs.gov/pub/irs-pdf/p463.pdf
