After years of spotting in Norway where SAS is the dominant airline and I cannot count how many times I have seen DC-9 and MD
-90 take-off, I can tell you that this is quite normal for the type. Not sure why though. Maybe the gears needs to be locked before the gear door closes so that if the hydraulic fails, it is still possible to retract the gears? Just a taught.
Dream no small dream; it lacks magic. Dream large, then go make that dream real - Donald Douglas