What happened to my Pittosporum?

Any ideas what happened to my Pittosporum? It was well established (7 years or so) and is only the ones along that fence line. Neither those nor the ones along the back fence (in pic 1) have been looked after very well in the last few months (newborn baby took over!) but only the side fence have died. I spoke to my neighbour yesterday and the only thing sitting along the fence on his side is a pile of mulch that he is going to move away.