Why do preppers or anyone need the ability and skill set to shoot a rifle up to 500-900 meters away?

First off, ‘sniper’ is a very misunderstood skillset. Sniping is not about ‘body count’, it is 99% ‘psychological warfare’. To know that ‘there is someone out there, with covert skills to stay undetected, while making various attacks (high-value-targets, nuisance shots, materiel destruction, etc.) can change complete ‘methods of engagement’. It can devalue some weapons, expensive weapons, quickly (fly a $5-million drone over a sniper’s ridge? Not smart). It can make one person into a feared company or even battalion, instantly. It is VERY cost-effective with equally-effective ‘manpower minimalization’. We won’t even consider that ‘if it weren’t valuable’, the military would NEVER spend millions if not billions in development of ‘extreme range weapons’ (from .50-cal sniper rifles to ‘beyond-line-of-sight-missiles’). Range-with-accuracy means DETERRENCE!
The problem is, not everyone has the physiological skills to BE a sniper…and many of those that do, are never professionally instructed in how to reach that level of skill (let alone, properly equipped to realize it).
Sniping is NOT a ‘primary offensive weapon’…nor a ‘Rambo skill’…it is a neurosurgeon…meant to drive a nail into a nerve at 1000-meters. Understanding what Sniping IS, is the beginning of understanding why you need the training, IF you have the skillset and equipment.