It appears that the subject of banning bunch riding two abreast is gaining momentum once again.
It is one of those situations that just because the law states that you can do something, is not to say it's wise to do so.
A bunch riding two abreast often overlaps the wheel in front effectively making it three abreast and drifting out into the adjacent lane forcing the driver in that lane to drift themselves out into the lane outside of them in order to keep clear of the rider(s).
Sadly some riders just do not get it, if the outside rider(s) is already nudging the white line then it's time to go single file, but keeping well out from the kerb so there's somewhere to go if a driver gets too close.
Many road rules were made when traffic on the road was only a small percentage of what is is today and riding two abreast was relatively safe.
Maybe signage saying "cyclists single file only, fines apply" or " cycling two abreast allowed" could be a start...I have a hammer and nails; just give me the signs!