Simple in normals if a lane gets outplayed they will probably stay outplayed. in normals you will have random skill factors of a wider range of skill, duo-s versus singles, and strategy disparity(cait+taric, versus two meelee at the most extreme end).
Therefore when a jungler that frequently plays jungle sees this they know that if a lane gets outplayed they will stay outplayed more than half the time. Also due to game mechanics if they catch your lane up, they just increase the feeder lane gold/kill resulting in a larger feed. Further due to how the feeder effect works the jungler is at more risk, and posses a larger risk of feeding a kill from himself(a kill worth far more gold than just letting the feeder die a couple times).
Therefore in normal queue, the strategy that under 'normal' conditions that is most optimal is to try to put 2-3 players on your team a little bit ahead and 2-3 players on the enemy team a little bit behind.
Obviously this will only work for normals, and even then it's not a "good" work in any way. However in organized team you actually have 5 minds to help the failing lane figure out how to come back, it is probably one of the worst strategies.
edit: Obviously if a lane falls a little behind, and plays smart it's better to help even in normal. But if you see something like 5-3 kills, or 2-3 in a lane. It's a case of WTF and stupid aggressive play. Seriously you should know in like 5 mins and before your death if you're going to be outplayed or not, not after a total kill and tower damage.