The answer to 'why is my vacuum grimy' is that a grimy vacuum is typically caused by a buildup of dirt, dust, and debris inside the vacuum cleaner. This can happen over time as the vacuum is used, especially if the filter and bag (or canister) are not cleaned or replaced regularly.
Some common symptoms of a grimy vacuum include reduced suction power, visible dirt and debris in the canister or bag, and a foul odor coming from the vacuum. To fix this issue, you'll need to clean the vacuum's filter and empty the bag or canister. If the problem persists, you may need to replace the filter or bag.