Why does increasin the m pof reactants increase the rate of reactions?

this is a chemistry question that is about reacting marble chips with hydrochloric acid. ths graph shows that as the m of the marble chips increase (volume of hydrochloric acid remains the same) so does the rate of reaction, but the surface area of the chips do not change. Does increasing the m somehow change the concentration of calcium carbonate or is there another explaination? Thanks alot.