Why doesn't the process of chemisorption form multimolecular layers whereas he physisorption with lesser force of attraction between molecules form multimolecular layer?
Chemisorption involves chemical attachment (electrostatic or covalent bonding) with the surface. Since there are a finite number of such bonding sites on the surface, the maximum occupancy is one monolayer.
Physisorption involves weaker (dipolar or dispersion) interactions, and additional layers might be able to attach to underlying layers via similar weak interactions.
It should not be assumed that additional layers cannot form following chemisorption, simply that these would not be associated by the same mechanism, rather through weaker interactions (physisorption). Such interactions are often termed "nonspecific" and preparation protocols may call for treating a surface to remove molecules associated that way.