It's not a credible enough threat to arm every police officer in the country though. Chances of it happening are low since terrorists are currently targeting large scale events and urban areas because they cause maximum fear and maximum coverage.
You can't have security for the sake of it if there's no credible threat. The cost and benefits have to be weighed up and currently youd say there is zero benefit even when ignoring the other arguments made in this thread.
The only terrorist attack in a rural area we've had in years is that lunatic who stabbed the mp over brexit.