Well, the US has a dual system; in the US everything eventually ends up being evaluated against a written Constitution (something the UK never had).

And if you look at SCOTUS, many Justices are essentialists (the most famous of which is Antonin Scalia); legal essentialism means sticking to the letter of the law.

So I think what I described is a reasonable explanation of the legal canary, at least from a philosophical point of view.