I've been seeing the teams do this whole ALL 5 OF US IN THEIR JUNGLE NAO GOOOOOOOOOOOOOOOOOOOOOOOO! Why do games start like that? What is the point? and why do the good players do this and the bad ones don't?

Its good for FB as a team is moving around you often can catch one by themselves. Teams that coordinate well usually do well. While other teasm that do not usually end on the losing side.

There are a number of reasons, one of the biggest being that your jungler needs the support and security. Generally speaking, the team that brings more people to a fight is going to win. 5 people catching 1 or 2 alone is bad news at any point in the game, even lvl 1. So even if your team isnt looking for a first blood, it makes sense to stick together until creeps hit the lanes. We have a huge advantage if our 5 man squad DOES catch someone, and were at a huge disadvantage if we aren't together and one of us gets caught.