Because July was the most popular perch month (because, like Indiana, much of the best fishing occurs then) and they got a lot of pressure to open it up. And at the same time, people also supported a spawning closure because it is a feel-good thing. Even though their new season protects the perch population less.
Both of those decisions (IMO, I was not involved obviously as it is a different state) were primarily driven by social concerns rather than biological
I don't think over-exploitation is the issue though, it's all about the recruitment bottlenecks and getting all the stars aligned in any given year to get the right environmental conditions (water temp, plankton bloom, currents, timing of the spawn, etc)
The following user(s) said Thank You: Lickety-Split
The South End provides useful resources and discussion forums for those that fish The South End of Lake Michigan for Salmon, Steelhead, Perch, and Bass as well as elsewhere in the Region and Chicago area.