I wish I could say I was being a clever journalist and leading with a question, but I honestly don't know the answer to this one. This is one of those topics that evades googling, because all the key words (east new york Brooklyn telephone power lines above ground) lead you astray, no matter the combination. But unlike much of the rest of Brooklyn, ENY actually has a substantial chunk of its grid above ground. You can find lines connecting bits and pieces elsewhere, but it's rare to see utility poles on every corner in a major city.
The presence of the lines makes shoe-tossing possible, another topic that I couldn't get to the bottom of because there are as many explanations for the practice (including some that claim to be borough-specific) as there are bloggers to write them up. The neighborhood was hit particularly hard by the crack epidemic (as I read in an article by Daily News reporter Denis Hamill in the book Brooklyn: A State of Mind), so perhaps in this instance the drug and gang explanations are relevant--gangs use shoes to mark territory, the presence of shoes notifies a user that crack can be bought nearby, etc--but I'm mostly inclined to the Occam's Razor explanation: kids goofing around throw shoes on wires.
If anyone from ENY has a particular explantion for the shoes that adorn the neighborhood's power lines, I'd love to hear it.