I would think manufacturers are pretty conservative these days because of some of the past issues with cars underperforming. My old 2012 Kia Optima Turbo for example always fell short of it's EPA rating, even with conservative driving.
A lot of people also don't seem to realize that if you drive a vehicle hard, it will get worse fuel economy. Some of my family members will tell me their cars get poor fuel economy, but rev it up to 4000 at every stoplight.