Tyler Falk has the answer:
It’s much more efficient to produce fewer, larger turkeys. And that’s exactly what the industry is doing. Last year, 45 million fewer turkeys were produced than in 1995. But in the past decade the size of the turkey is getting bigger, meaning larger turkeys at meals and more opportunity for waste.
Brad Plumer adds:
Of course, there are also a few not-so-savory downsides to hyper-efficient industrial turkey farming. As Lynne Peeples reported last year, tens of millions of turkeys in dense factory farms are fed a diet that includes low doses of antibiotics, which help animals grow faster for still-mysterious reasons. And public-health experts worry that these crowded farms could, in turn, help spread new strains of antibiotic-resistant bacteria.
Chart from (pdf) the U.S. Department of Agriculture.