110.75x68 Mauser introduced in 1920s.
I think we're looking at an era when the medium bores dominated the market especially cartridges like the 375 H&H and the 9.3x62. However the key was probably that there were enough cartridges to do the job and no need to create the latest greatest variants. Having a restricted range of cartridges probably also helped supply in far flung regions of Africa and India. The British restrictions on 45 calibres for India may have still had an effect.