Answer:Due to the pressure difference created by rotating fans.
Step-by-step explanation:
In most of the vacuum cleaners, there is an area which is of disc shape and it is in right next to the motor. There are several fans within the disc that spin at a very high velocity.
The blades will push the air outside of the disk.There is no air in inside of the disc and air pressure creates which pushes air inside the disk to replace the missing air.
So motor is pushing the air outside and to maintain this pressure the air is pushing toward inside with dirt.