Why polar solvent favours SN1 mechanism ?

The S_N1 reaction is a substitution reaction in organic chemistry. "S_N" stands for nucleophilic substitution and the "1" represents the fact that the rate-determining step is unimolecular.^[1][2] Thus, the rate equation is often shown as having first-order dependence on electrophile and zero-order dependence on nucleophile. This relationship holds for situations where the amount of nucleophile is much greater than that of the carbocation intermediate. Instead, the rate equation may be more accurately described using steady-state kinetics. The reaction involves a carbocation intermediate and is commonly seen in reactions of secondary or tertiary alkyl halides under strongly basic conditions or, under strongly acidic conditions, with secondary or tertiary alcohols. With primary alkyl halides, the alternative S_N2 reaction occurs. In inorganic chemistry, the S_N1 reaction is often known as the dissociative mechanism. This dissociation pathway is well-described by the cis effect. A reaction mechanism was first proposed by Christopher Ingold et al. in 1940.^[3] This reaction does not take account much on the strength of the nucleophile unlike the S_N2 mechanism.