Organic Chemistry Question-The reactivities of acid chlorides decrease as the R group is more substituted, why?

I wanted to know if this is because the more substituted the R group the more electron density will shift to the carbonyl carbon thus adding to the stability of the functional group and slowing the reaction rate. Since I know the more stabilized a compound is the less reactive it is in regards to nucleophilic acyl substitution of carboxylic acid derivatives.