Well Spotted Mate:). Yes this is a Malvern star Auto byk...byke.
They were made for about 15 or so years.

You have a good point...why? I guess maybe for the same reason as they are popular in modern times. Not having been around back then I cant attest to their efficiency, but I have owned one from this period and it was more powerful than youd think.

At a guess I would say, cost, weight and perhaps safety (meaning less speed and risk of injury over a motorcycle. If youve ever ridden an old bike of the 20, s to 40s you will understand my meaning.
My Harley was a pup (350) but they also came in V twin and some exceeded 1000cc. Ive ridden a side shift 600 and it was scary enough. Maybealso the use for females of the era was more appropriate, and the fact it could be easily pedaled or walked....Pushing a motorbike of this era is not much easier than todays models.

Keep in mind also that power units ranged from (av) 50 cc 70cc 98cc up to 122 cc...these were the more common sizes. So power for some variants was not an issue.

I guess more research would be required to see if they were truly viable, but I do know they were very popular.

Also the war may have had an impact due to materials over a larger Motocycle, making it a more viable form of transport at the time...This may be proved by the date range, late 30's to early 50's

As you may know the WLA Harley models were mostly earmarked for war.

I personally just find them appealing as I do most thing from this era.

Yes Victoria is a funny state, they can go from one extreme to another. ..lower speed limits but less stringent on Automtive applications like Engine capacity. You use to be able to have any mod you wanted and Vic is the muscle car capital of Aus...As is Canberra.

One other point as far as im aware, is that you didnt need a bike license exclusively. ..You could legally ride these with a normal car license...

Anyways Im aiming for a 98cc or higher...cause I am a big boy of 6 6" but its more about the restoration than the ride, as Eventually I plan to get another Pre 30's Harley. ..just have to be patient