Think of it like a team sport. I don’t know the current trends, but back when I played LoL, teams typically sent a tankier AD top, a mage mid, a ranged AD bottom with a support, and one jungle. The idea was to spread XP around in the most ideal way while also having a roster balanced between different skill types. Much like a team sport where different types of people have different roles. Now, it didn’t mean that there was no change to that, and it didn’t mean that nobody ever left their lane, but you typically played your role with little deviation early game.
I’ve played a few games of this recently where people load up in middle, or just seem to pick some random lane every time they spaw. Now I don’t know the game mechanics 100%, but to me that would be like a hockey goalie just suddenly skating out to play forward because he feels like it. I try to stay patient because it is only a game, after all,and I can’t expect everyone to adhere to any kind of strategy, but when you’ve experienced great team cohesion and lane discipline, experiencing the inverse can be very grating.