This question was heavily debated. People gave different answers, and this is not easy to ask. Needs some in-depth analysis.

Most importantly is that this is a thermodynamic issue.

many sources answered it based on rate of evaporation which is not the case.

From thermodynamics, the solution needs to gain maximum entropy. Therefore, the dissolved solute particles demand more volume to swim in. Thus more solvent molecules will try to come back to liquid to achieve this. Therefore, less solvent evaporation should occur.

Do you agree?

The solute solvent interactions on adding a solute increase and hence the solvent which was earlier readily available for evaporation cannot vaporise that easily. Hence, the vapor pressure also gets reduced as compared to earlier.

Dear Dutta

If "solvent-solute attractive forces becoming larger" is the reason, then the next question is:

There are solutions which have smaller solute-solvent forces. Such solutions typically have positive enthalpy of solution. 

Assuming your answer is correct, then in the second type solutions (with positive solution enthalpy) vapor pressure of solvent should increase by solution. Which is not the case. Solvent vapor pressure is always lowered by solution (in both types of solutions, with either positive or negative values for solution enthalpy).

The reason must be otherwise.  It must be based on entropy (chaos) of system. Assume there is a pure liquid solvent in equilibrium with its vapor, and assume that we then add a non-volatile solute to the liquid solvent,   the solute molecules will need more space to swim inside.  That is to maximize entropy (chaos). Therefore, some vapor molecules will then be pulled back to the liquid to allow more room for solute to swim in, and to maximize entropy (chaos).

A new equilibrium is then established with smaller solvent vapor pressure. That explains Raoult's law in a simple model. 

If you do not agree, we will then need to go into mathematical equations about entropy and solution chemical potential. 

Who agrees with that?

@Hilal.. I do not completely understand the correlation between the swimming space required for the solute molecules and the entropy maximization. The randomization of the system would anyway be increased when the solute molecules would be added, Isnt it?

Dear Dutta

Here the logic is:

If solute molecules have more space to move in, they will then have more degrees of freedom.  That gives more chaos and more entropy to the system, and makes it more stable.

Do you agree now?