When you pitch the story to an editor, you need to go into all the details of the story, background; interactions; relationships and make sure to give them as much as possible to find your niche'.
A blurb on the other hand is totally different, this is your selling point. Here you need to be short, sharp, punchy and do NOT forget the most vital part (in my case), leave unanswered questions to draw the readers in. Once you are on the shelf, remember the 2 minute rule - that is your selling time - beyond that and you lose the sale.
An analogy in cooking :-
To the editor; you have to give the recipe including cooking times
A blurb; is the taster - we have all dipped our fingers in the mix to taste it - that was the blurb for the cake.