When Take Two and Microsoft struck a deal in 2007 that GTA 4 is getting two DLCs exclusively for the Xbox 360, everyone including Microsoft and Take Two were expecting a great success for these DLCs. But according to the sales figures for these DLCs, it seems that this wasn't what they hoped for.  
 
 
 
Take Two CEO Ben Feder thinks that the late release of the DLCs after the original game has caused the game to suffer in the sales department:  
"Both we and Microsoft believed there was a big market for GTA 4 episodic content and some factors affected their performance.  
Both were released significantly after the launch of the core unit and therefore weren't able to leverage GTA 4's initial marketing campaign and initial launch fervor."  
With the Lost and the Damned released after 10 months of the original, and The Ballad of Gay Tony after 18 months from GTA 4 initial release, I guess that what he claims about the reason of the poor sales for the two pieces of DLCs might be correct.  
Though he admits the poor sales of the DLCs, he has high hopes for better sales in the future for these DLCs:  
"There's very little precedent for this type of episodic content at the price point we offered it. And so we're confidant that these titles will continue to have a long life just as we've seen a long life from all of our other prior GTA releases."  
It's really a shame, considering that both DLCs are of high quality, especially the second DLC, The Ballad of Gay Tony.