It is an over simplification but the 'secret' to all this appears to be the manufacturers [AH] decision to offer a system rather than just the airframe.
Robinson did the same thing with their R44 Police [and later R66 Police] in that they provide a standard law enforcement airframe at a keen price. Mess about with the factory specification and you will pay a bigger price. You can change the EO/IR and searchlight if you will but everything else is off the menu.
Pretty much all that went before was piecemeal and almost every aircraft completed in the 1990s was a new adventure in how to do it wrong. Look at the UK NPAS fleet. Every one of the aircraft was designed by a different organisation and sometimes put together and modified by other organisations. That creates difficulties for installations, engineers maintaining and the ability of pilots to operate differing aircraft across the fleet.
They are currently trying to set one or two standards of EC135 to reduce the problems but only a new common airframe will eventually enable it to happen.
It is the same in some units in Germany. The NRW have two very different standards of BK117 and the EC155 that pilots need to be proficient on. When the fleet is 100% H145 the pilot training costs will fall and the ability of the pilots to know and understand their aircraft will greatly increase.
It is the same in the USA, nearly all their many H125s come out of anything like a dozen completion shops.
The 'other' manufacturers have not yet grasped that concept - and may never do - but the prime decision lies with the police in that they need to decide what they need from their fleets and minimalise the number of types they buy.
A Federal Police fleet of 100 can afford to have 2-3 types but smaller fleets simply cannot have the luxury of 'one of these' 'two of those' and 'one of those' especially if that means having airframes from different manufacturers as well.
On the last point, safety also comes into this - I expect there is little worse in an emergency for the pilot of three diverse types having to even spend a millisecond deciding whether he/she is in a Notar, left tail rotor, right tail rotor, Feneston or clockwise or counter clockwise main rotor..... as the earth gets closer and closer....