Alkenes and arenes both are unsaturated and electron rich. Alkenes undergo addition reaction to give more stable saturated product. In this reaction hybridization changes from

sp²to sp³.

Arenes are stabilized by resonance with delocalization of electrons. On addition reaction to the double bond of arene, a product is obtained which is not resonance stabilized whereas on substitution the resonance stability of arene is maintained. Thus, arenes prefer to undergo substitution reaction while alkenes prefer to undergo addition reaction.