Using a longer tube, the manufacturer could increase focal point resulting in a very precise focus, but you will lose depth of focus. That means if you’re hunting and an animal is approaching you’ll be fiddling with your AO (or side focus knob) instead of simply tracking it.
Of course the scope would need to be designed that way and a longer scope does not immediately equate to a longer focal point, only that it’s possible. Designers understand their audience (hunters or target shooters) and design optics to suit typical needs.
For most purposes it is weight savings and eye relief as previously mentioned that determine which length is advantageous.