The answer to 'why is my vacuum dusty' is that a dirty or clogged vacuum filter is the most common cause. Over time, the vacuum's filter can become blocked with dust, debris, and pet hair, reducing suction power and allowing more dust to be blown back out. Other potential causes include a full dust canister, a clogged hose or attachments, or a worn-out vacuum motor.
To fix a dusty vacuum, start by checking and cleaning the filter according to the manufacturer's instructions. You may also need to empty the dust canister more frequently, especially if you have pets or live in a dusty environment. If the suction still seems weak, check for clogs in the hose and attachments, and consider replacing the filter or even the entire vacuum if it's very old and worn out.