Well, according to Omega advertising from the time, these watches were meant to be worn when skiing in the Italian Alps.
Due to the possibility of springbars failing if the watch was caught on a ski lift rail, or the edge of the bar at après-ski, and the risk of the watch falling off, fixed bars were used that wouldn't fail, maybe cause a dislocated wrist, but the watch was retained.
Fixed bars were used up until recent times on many military watches for these reasons.
Seriously, I think it was just a transition phase between the welded lugs on early wrist watches and the modern springbars.