Sometimes there are long term cycles of certain animal populations that are the result of several factors. Seemingly small changes in weather, land use practices, and predator numbers, etc. can have huge affect animal numbers.
An important figure in the survey is poult count(s). If the DCNR is seeing lower nesting success (or lower poult numbers), that may be one reason for advocating a reduced limit in spite of hunters seeing or hearing a "normal" amount of turkeys. Hunter success can be used as a general indicator that something is changing, but it is too variable to use as a definitive measure of game animal numbers.
Missouri used to have a huge turkey population, but in the last few years it has been reduced due to lower nesting success. It's coming back but not like the "old" days according to some MO beard-busters I know.