I am surprised by them moving the season a week later though. Does anyone know the reason behind the change?
I don't think there's really been a change. The eastern Washington elk season opened on the last Saturday of October in 2025, and in 2026 it opens on the last Saturday of October also, which just happens to be October 31.
Similarly, opening day of deer season was October 11 in 2025, and will be October 17 in 2026.