I was thinking of British TV when I posted that so not too surprising if its mostly a thing there.

To add an additional exception here, police in Northern Ireland are routinely armed, but obviously enough there's reasons there.

I think it’s more common in Europe since those are large targets for terrorism. Plus if you have a distinct “armed police” they are more likely to be heavily armed.

Also, I think most police outside of major cities in the USA all have ARs in their patrol cars now. I remember when my cop buddy was complaining about five years ago when they took his car shotgun and gave him an AR instead.