Your cars and wheels always look good and detailed, and that's the problem. The level of detail and smoothness doesn't fit well with the rest of blockland. Limit your circles to 8-16 edges, give the body less curvedness, and extrude out important features (like taillights and door handles) to give it more of a blockland feel. The reason that modelers like phydeoux and filipe were/are so successful is because the detail on their vehicles were/are on the line between detailed and blocky. If you can get your vehicles right on that line, you will have a nice lineup of vehicles you made.