From what I've seen, there is definitely a lack of incoming funds. Many of their members are young teens that have little or no money (only ice cream money), are elderly people living on a fixed income, are pioneers who rely a lot on assistance from others to even meet their own needs, or are living in third world countries where $100 would be a weeks or even a months worth of pay.
I think the lack of incoming funds is the largest reason for the reduction in printing. Even though the labor is free, the cost of materials, electricity, and maintenance (repair parts, etc.) are not. If they were being truthful back in 1990 that $0.25 per WT or Awake just covered the cost of printing, then today (with inflation) each magazine would cost ~$0.46 and each set would be ~$0.92. If each congregation is receiving well over a 150 sets of the public edition and around 100 of each study edition, each congregation is costing the org ~$184/month just for printing the WT & Awake. Add in the books, brochures, and special order items and that number could easily double.
The amount I have seen collected each month seems to fall short of covering those costs. The fact that several letters have been sent to the congregations asking them to reduce their standing orders and that many congregations (mine included) had their orders (even of special order items) automatically reduced seems to indicate that WTS understands that the printing costs are outpacing their donations.