When I was running communications for Williamson County, I was big on transparency and public accountability. But then again, that has a lot to do with why I'm not there anymore.
Then (just a year ago, about exactly) only sensitive Sheriff's Office operations (SRT, Narcotics, etc.) and Leander PD were encrypted (and I had no influence over Leander.)
Non-compliance with NIMS protocols may be part of the reason - if you don't want anyone knowing you're not complying with requirements of all those federal grants, then you don't want them listening. Note that comment does not apply to Georgetown - they've always been good about NIMS compliance.