No one has really given decent reasons tho.
Here are a few…
Stronger wheel (ok you may not need/notice it but it is true)
Already have the hub built into a wheel (maybe they are a SS’er who wants some gears back for a bit? like er… your pompy?)
Hope SS comes with steel freehub already (so much cheaper than buying a separate steel freehub for a normal Pro2)
I ran a Pro2ss for a while, swapped it out for a normal Pro2 as i went to a frame with a 12mm axle and you cant make the Pro2ss 12mm compatible.