Because it’s random that CH3CH2CH2CH2CH3 losing a (·H), so by reaction with Cl2, it can
form many isomers, such as CH3CH2CH2CHClCH3, CH3CH2CHClCH2CH3,
CH3CH2CH2CH2CH2Cl, so a poor way to prepare 1-chloropentane.
While for (CH3)4C, each of the H atom are equivalent. So no matter which one be substituted,
only one product, (CH3)CCH2Cl, can be prepared.