Most of a tractor-trailer’s stopping power is split between the trailer brakes and the tractor’s drive tandems. If there is not enough weight on those axles, the tires can’t grip the pavement properly. If I apply too much power to the brakes the wheels can start bouncing or just lock up and start skidding if the ABS system is acting up.
Most tractor-trailers you see on the road in the US are designed to weigh 60,000 to 80,000 lbs (~ 27,000 - 36,000 kg). For comparison, a Honda Civic weighs roughly 3,000 lbs (1360 kg). Every system on the truck is designed around moving that amount of mass safely. With an empty dry van trailer your looking at closer to 30,000 lbs (~ 13,000 kg). Makes a difference in performance. Ride is rougher, takes longer to stop.