Since it always was a seasonal cycle, and the ascendency followed this behavior, we averaged the ascendency over 365 successive days (duration of one year) in the oscillatory phase.
You see, most clothing retailers even today function on a seasonal model with huge production runs, and towards the end of each season they heavily discount the clothes they didn't manage to sell.
A couple other states have grappled with proposals concerning seasonal time changes, but even among those who want to eliminate them, there's still a debate over when to do it.