Tautomerism in alkenes
In order for tautomerism to occur, the enol must be deprotonated, so as to allow the negative charge to come down, kick the pi bond of the C=C bond, which will bond to a proton. Hydrogen atoms on oxygen are much more acidic than hydrogens on carbons because of the electronegativity differences between O and H. Thus, the deprotonation does not happen in alkenes.