I've wondered if there is a seasonal component to this.
People stay up later and do more stuff in the summer months, so they are more tired, busier and distracted. I think lack of sleep and overscheduling plays a huge part in this type of tragedy.
I forgot my youngest child on the kitchen table once when she was an infant. We had come home late at night and I had taken her in her carrier out first and set it on the table, then went back to carry in her sleeping sibs and put them in bed.
I woke up for her 4 a.m. nursing and found her still sleeping soundly in her car seat on the table.
It was in the summer, too.