All nations within the Anglosphere (US, UK, CA, AU & NZ) have JD imposed towards citizens. I know that the US & Canada both inherited that from Britain, which explains why they have it. However, should it be entirely only the judge making the conviction (some countries operate on a lay-judge system meaning juries aren’t used, such as Finland or Japan for example) rather than leaving that decision up to jurors?


Jury duty exists because of the jury trial.
The use of the jury trial exists as a counter to the state potentially obtaining control of the courts and using it to impose criminal legal penalties on those it dislikes. You’ll notice that Donald Trump has had investigations against and can have charges issued against a lot of people that he doesn’t like. But a prosecutor then has to be able to successfully make their case to a jury. Not much action on that front.
Some “want to avoid” scenarios include the legal system under the Nazis:
https://en.wikipedia.org/wiki/Law_of_Nazi_Germany
Or the Star Chamber:
https://en.wikipedia.org/wiki/Star_Chamber
you explained it well.