You answered your own question. Because they're encrypted. They have been since they made the switch to a trunked system. When I lived in Saint simons island Georgia,I could hear them when they were on UHF frequencies,once in awhile.Why can't JSO be monitored? Unless they're encrypted, or the database is wrong, the systems in that area are Smartnet or SmartZone and should be very monitorable.
Of course, the SLERS system isn't monitorable.