The answer to 'why is my vacuum filthy' is that a dirty vacuum can be caused by a clogged filter, full dust cup, or buildup of debris in the hose and brush roll. Over time, dust, hair, and other particles can accumulate in the vacuum, reducing its suction power and efficiency. This can lead to the vacuum itself becoming dirty and distributing more dust and debris around your home.
To fix a dirty vacuum, you'll want to first empty the dust cup or canister and clean or replace the filter. Check the hose and brush roll for any clogs or buildup, and clean them out. Regular maintenance like this will help keep your vacuum working at its best and prevent it from spreading more dirt and dust.