Excellent question! First of all, if a home does not sell, it usually comes down to Price, Product (your home) or Pitch. (Marketing.) The good thing is, you were able to get it leased!
Realtors are calling you because you are a hot prospct fo future business. As to their answer to your question.....a good Realtor will assess their buyers' needs, then help them find an appropriate home based on those needs. As a Realtor, if I have a home that meets those needs, I certainly show it to them, but I do not limit them to seeing only the homes that I have listed.
Next time around, interview 3 Realtors. Explain what happened the first time around. ASk them how they would market your home differently to get your home sold. Listen carefully. ASk fo examples. ASk for references from other sellers.
Make sure you hire a Realtor...not just an agent...there is a difference!