this is like asking why 3/3 (technically 0.999999999 and so on) 1/3 (0.333333333 and so on) and 2/3 (0.666666666 and so on) is converted to one, its because the margin of difference is infinitely small and cannot be defined so in a way it's pretty much skipped.
1-(1^-10^-1) is 0.9 to infinity
1-(1-10^2) is 0.99
1-(1-10^-3) is 0.999
1^(1-10^-infinity) IS 1-(1-10^infinity) but still not 1.