Why so few photos of the wreckage
Actually, there is probably a very simple answer.
Suppose BEA picked several interesting photos from those taken and released them to the world primarily for the purpose of showing that they had indeed found the wreckage.
Suppose then that a sharp eyed individual examining one of the pictures said "That shape over there, I think it is human remains" and then publishes that statement online. Whether or not the item was correctly identified by the poster, there would be an embarrassing and distressing scandal.
Each picture released has the potential for causing such incidents. You can bet that those photos that were released were carefully screened to be easily identified and non controversial. With the workload the BEA staff has now that data is starting to flow in, they will be in no hurry to release any other pictures.