The Petersen Automotive Museum in Los Angeles has a current exhibit entitled "What were they thinking"? They thoughtfully provided cartoon cutouts with possible answers...
Motorized skates used a 1 HP gasoline motor strapped to your back, a flexible shaft to the rear wheels on the right skate, with a hand-held control for the clutch and throttle to get going up to 17 MPH.
The AMC Pacer of the mid-70's was low-quality and turned off buyers with the "fishbowl feeling".
The 1958 Toyota Toyopet just misjudged the market.
Thankfully only one Scripps-Booth Bi-Autogo was built, in 1913. The 3,400 lb motorcycle had small wheels that would stabilize it at slow speeds or at a stop.
The US Army purchased 2 full-size units for testing in the early 60's. Not surprisingly, they failed. Large size, slow speed, and ponderous handling.
The 1950 Edsel Citation is now a collector's dream, though originally it was low quality and sort of oddly styled.
The 1947 Gregory looked conventional, but had the engine in back and drive wheels up front. This requires a large and heavy driveshaft...
The 1935 Chrysler Airflow was fairly bland under the styling.
The Chevy Convair had an air-cooled engine in back which affected weight distribution, and the independent suspension was flawed. It was a target of Ralph Nader and consumer-protection groups. It was killed off in 1969.
A 1923 Chevrolet used a lot of copper fins around the cylinders on the air-cooled engine. Production shut down after about 500 were built, and most were recalled...for cooling problems.