Their not hiding anything.
Well, yes they are, but it's not some cloak and dagger conspiracy either (as you noted later in your post).
Let me explain. When an agency encrypts, they sell the act as securing their operations against "bad actors" that could/would use the radio traffic to gain a tactical advantage over the agency. While true, to an extent, routine dispatch traffic rarely gives that advantage to "bad actors" so long as agency practice is to move "hot calls" off of primary dispatch to a secondary, secure, channel. This is simple to do, yet many agencies fail to do it (many reasons). The
real reason is to keep radio traffic out of the hands of the public for as long as possible in the event the agency's actions are called into question, which in today's climate, is an absolute certainty.
...all radio and bodycam footage is FOIA’able
This is true, and an important point to keep in mind. However, with FOIA requests, the agency whose actions are being called into question can, and will, take as long as it possibly can to release such information. How long depends on how...
skilled...their legal eagles are at holding up the process.
As expected DPD traffic is normal, no coverups or conspiracy’s happening there either.
Another important point. Agencies that have gone totally dark (as a few I'm personally familiar with) aren't suddenly in the business of subverting the Constitutional rights of citizens nor preparing for the rein of the Dark Lord of the Sith. They are simply trying to secure their operations and it's much easier to just encrypt everything than pick and choose which channels to leave open, which to encrypt. The people making these decisions are at the Command Staff level, know little about radios beyond how to operate them, and have "bigger fish to fry."
Locking out the public, however, is one of hundreds of tiny steps in that direction. In other words, death by a thousand paper cuts. Total encryption isn't the end of the world, but it's not something to just shrug off either.