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As opposed to the carbon-carbon double bond, introduction to the molecule a carbon-oxygen double bond never results in the formation of cis- or trans-isomers.
$C=O$ group is stronger than the $C=C$ bond.
$C=O$ group is more polar than the $C=C$ bond.
Oxygen is connected to only one atom,
Rotation around the $C=O$ bond is too difficult.