[iScience]

why do SN1, SN2, E1 and E2 reactions proceed faster with more nucleophilic reactants?

[clarkstill]

What an odd question.  The answer is basically "by definition" - saying a reagent is more nucleophilic is precisely equivalent to saying that it's reaction with an electrophile will proceed faster.

However, your statement that "SN1, SN2, E1 and E2 reactions proceed faster" is not true.  Both SN1 and E1 reactions do not involve the nucleophile/base in the rate-determining step, so the nucleophile does not affect the rate.  Also, to be a pedant, the E2 reaction requires a base, not a nucleophile.  Nucleophiles can be basic, and vice-versa, but this is not always the case (e.g. I- is a good nucleophile but a terrible base).