Just a guess regarding shipping, but a general observation that probably applies there as well: appearing significantly more careful than average will make you seem weak to your peers.

On top of that they would hate you for demonstrating that it could be done better, like being the guy who does not drive n over posted speed limit (n varies from jurisdiction to jurisdiction, but is a positive number almost everywhere). And bosses probably expect speed and care, in that order, but that isn't the main mechanism.