The issue, at least in the US, is that we're expected to be self-policing. The FCC, as an extension of the IRU, puts severe limits on speech over the airwaves. I'm sure the UK is similar. When encrypted information is transmitted there's no way to know if the information is in compliance. For example, imagine an ambulance service installing ham radios in all their vehicles then instructing their drivers to get amateur licenses. They could start using the local repeaters for business communication and no one would be able to prove it. The ambulance company could say they were conducting a drill, or that the drivers were just rag chewing during their downtime because they enjoy the hobby, whatever.
BTW, in the US, amateurs have been setting up DMR repeaters. Most of these repeaters are capable of encrypted communications. It's just a setting in the software.