Why the decrease of $25.46/year for the same amount of levy?

The payment is a fixed amount divided by the total market value of property in Teton County, so as market value increases, the tax impact decreases. Market values for Teton County
(Assessor, Teton County, Idaho):
FY2019 net taxable market value: $1,867,236,168 FY2017 net taxable market value: $1,618,928,300 FY2015 net taxable market value: $1,392,779,520