Because the stepper motor might have plastic in it, and the petroleum based WD-40 could degrade the plastic? Also, WD-40 is more solvent than lube - it does a great job at breaking down gunky oil-based lube but not such a great job at being a lubricant itself.
I do NOT recommend Wd40. Use Silicon grease instead. do not use any lubricant that's petroleum based.
Because the stepper motor might have plastic in it, and the petroleum based WD-40 could degrade the plastic? Also, WD-40 is more solvent than lube - it does a great job at breaking down gunky oil-based lube but not such a great job at being a lubricant itself.
Well, congratulations.