The more intuitive reason that substances labelled with (aq) are taken into account for shift in the state of equilibrium:
Let us consider activity as concentration of the substance for the sake of this question.
The concentration of solids and liquids is taken as unity while studying equilibrium because they are incompressible in most cases. So if you add say 100mL of NaCl (l) to 1000mL of NaCl (l) present already, then that 1000mL still takes up the same volume in the reaction mixture while the new 100mL takes up new space(volume). Also note that 100mL and 1000mL are comparable here.
On the other hand substances labelled as (aq) are taken in small quantities (for example: 5gm) and spread throughout the vast quantity of water (100mL - 2L). Thus if you add more of the former substance it will enter the same water and the population of this substance would become more in the same volume of water. (Eg. 5g in 1000L water is 0.005 g/L ratio to which if again 5g of that substance is added it becomes 0.01 g/L ratio)
Hence in case of the liquid the concentration remains same and for the substance it increases.
Shift in the equilibrium is shown by reaction quotient
Qc =[D] (aq) [C] (aq) / [A] (s) [B] (l)
As explained above solid and liquids get concentration unity while aqueous substance has variability. Thus [A]=[B]=1.
Therefore reaction quotient (which is a projection of shift in the equilibrium) takes the expression
Qc =[D] (aq) * [C] (aq)