In the end it all comes down to risks vs benefits assessments. Is it worth for an operator to legally allow circling approaches when its pilots never have the chance to fly the maneuver in the sim or on the line considering the network structure ?
Some might argue it is better to leave an extra open option considering the fact that nobody would end up flying a circling approach if better options are available... but in that case some form of consistent training is required at least in the sim. It is not acceptable in my opinion to allow such a basic flight maneuver (in the end that's what a circling is - it becomes tricky only on a large transport airplane) with no recurrent training whatsoever.