They could counter with an increase in the length of SC periods, but that has negative consquences for them too. Primarily in that it pushes that pilot's future availability for a rotation or SC continually later until you reach a point they are practically useless on a reserve day. The 6 hour SC blocks work perfectly with the 18 hour break requirement to keep a pilot on the same SC time for their entire block (unless given a rotation obviously). With 9 hour blocks a 1400 SC pilot can't start SC on day 2 until 1700 then on day 3 until 2000, and so on. Plus it's not super common but espeically with a morning SC 9 hour SC (or the 2359 one) you could get into issues bumping up against the RAP+FDP limit.