Sudden winds - if Boeing recommended the highest possible flap setting almost every takeoff would be Flaps 15 or 20/25(depending upon individual company Ops Specs/SOP's).
The only time we didn't use Flaps 1 is if Flaps 5 allowed more weight for takeoff. If Flaps 5 didn't work we'd use Flaps 15.
At normal length runways I've never seen a 737NG takeoff with Flaps 15. It's typically F1 or F5.
Based on that I'd be surprised if Boeing recommended using the most flaps available. No U.S. airline appears to be doing that and neither are the foreign 737NG departures that I've observed.