it's simple, light ability for hunting in late evening hours. I'll try to explain why there are huge objective scopes in Europe, and why they are populare.
Before it was always the 8X56mm who where the light king, 3-23X56 loosing a tad light ability due to more complex building compared to a fixed lense.
There is a formula on this light ability, if I remember correct it's this way, 56mm divided by 8X zoom = 7.
7 is a number where your eyes can see most in dark light. 42 mm divided by 7 gives 6X zoom as ideal. 32 mm gives 4,5X zoom as ideal. You see the picture where I am going now. 56mm is the king, going down to 42 it has less ability to let light come through for hunting late evening hours.
Decades ago they develop red dot for their 50-56mm lenses, not made for daylight, the dot is so weak that you can not see it in daylight, it was made as helper in the real tricky situations where it was so dark that your couldn't see the cross, but you could see the countur of the deer. You turned it on, slowly and not so much that it would blend your vision, and you could set a safe shot. I've shoot a couple deer in a situation like that, also a beever on 300 metre distanse with my 30-378 late hour.
I've had Doctor 1,5-6X42, aspherical lense, and a Zeiss Victory 3-12X56 on the same time.The huge lense provided me with at least 30 minutes extra shooting light, pluss the extra shooting light time with the red dot. There is a noticeable difference from 42mm to 56mm when it comes to light ability.