My understanding is that this is also a money thing?
Trial by jury is expensive and slow. If you're the UK, which is a country that's slowly ratchetting the state onto more and more of a shoestring, it's unthinkable to actually fund as many trials as you'd like to hold, and that has very much been a brake on mass arrests over the last five years or so.
Trial by magistrate is far cheaper and faster. It makes mass arrests affordable, which means that the UK can have carceral brutality without having to properly fund that carceral brutality.