Hello FerRory,
My English is bad for this kind of subject. But I will have a try.
The topic you started is very good. But I guess, none of we guys are toy historian.
The 1:43 scale which is probably the most popular today... was started as an accessories for toy trains of the same scale (O scale I believe). So brands like Dinky, Corgi, Marklin etc... have adhered to 1:43 scale mouvement when they saw it was a nice scale.
However, the 1:43 scale was not the first one, few decades back... there was many scale sizes.
Marcel Brossi.