Haloarenes (like chlorobenzene) are remarkably unreactive toward nucleophilic substitution compared to haloalkanes due to several factors:

1. Resonance Effect: lone pairs on Chlorine are conjugated with the $\pi$ electrons of the benzene ring. This gives the $C-Cl$ bond partial double bond character, making it shorter and stronger.
2. Hybridization: The Carbon in $Ph-Cl$ is $s{p}^2$ hybridized (more electronegative), while in $R-Cl$ it is $s{p}^3$. The $s{p}^2$ carbon holds the electron pair of $C-Cl$ more tightly.
3. Repulsion: The electron-rich benzene ring repels incoming nucleophiles.
4. Phenyl Cation Instability: $S_{N}1$ is impossible as the phenyl cation is highly unstable.