That's a very small proportion of the overall police force that carry. It's got to be to do with the attitude around weapons.

There are about 7000 armed police in England and Wales. Their weapons are kept in safes in the back of their cars, they need to have a very good reason to be carrying one, let alone actually using one.

I think in the UK, despite the police closing ranks when threatened (I don't think we have this as bad as the US either) an officer that drew a weapon on a suspect that they had no reason to think was armed (and was only suspected of underage possession of alcohol) that officer would be subject to some sort of disciplinary action.