I can think of 3 possibilities for the increase in die wear and breaks seen on pennies during that era:
1) Something different about the steel alloy used for the dies and the annealing-hardening process that wasn't optimized for the alloy.
2) Use of greater strike pressures to improve coin quality.
3) Poorer quality control at the mints, allowing more of these coins to escape into circulation.
Hope someone more knowledgeable can help... we're curious!