Back gear was initially not a cheap compromise geared head system,back gears were in use many many years before geared heads. Engineering lathes and other machine tools were driven by flat belts,which cannot drive a machine tool spindle at low speeds and transmit sufficient power , so some means of positive drive was required,in early victorian machines sometimes worm drive was used and later on ,large lathes had the rear of faceplate fitted with an internal gear ring driven by a pinion,then the back gear came into use in later Victorian times,simple to make and maintain ,easy to lubricate due to the low speeds in use at the time with plain carbon steel tools,early milling machines also used back geared spindles. One problem was that lathe opearators tended to loose their fingers in the gears,one of the earliest factories acts was that back gearing had to be fitted with guards. Aso around this time the very early automtive transmissions went through the same development process of open belts,open gears,open chains . When higher speeds were required for HSS tooling,better lubricationwas also required so gear boxes were developed though the changes took a very long time no doubt due to cost, both the manufacturers factories tooling and what the customer would pay.