I wish to know why adcs can powerspike after 2 and sometimes even 1 item

That's really enjoyable to see your bot win the lane hard in early game and then once you try to engage on kogmaw that was behind and has only guisinos and berserker greeves as a fed fighter you get melted to the point you have to back off nearly immediately or you get melted before you actually kill him. And from then every single part of an item he buys he gets few times stronger. Can we do something with adcs getting their ridiculous powerspikes at 1 or 2 items? Seems fun to see enemy twitch getting destroyed, but once he buys runnans hurricane and pickaxe he suddenly melts your team in the fight after being so behind that you were diving him under second turret no problem. Same goes for e.g. kayn. The guy was 0/3/0 with 100 farm at 20 minutes and had only warrior enchancment and phage. He takes away more than half of my hp without ulting and I had 116 armor which is 54% reduction. He had not a single armor penetration item. When I put a champion behind to that extend I expect that champ to be useless and not destroy me or my whole team with barely any items.