I don't really understand the theme of this game

When I watch competitive games and play games with groups of 3-4 of my friends.. it seems the game is just about passively farming until someone gets caught by one of the many 100-0 combos.. and then the team that gets the catch snowballs out of control.

Objectives (towers, dragons, barons) get blown over by a small breeze.

Ganking lanes as a non-jungler, and even some junglers, becomes detrimental because it's more worthwhile to just sit back and farm and getting those kills isn't all that punishing or rewarding.. so why leave lane? Especially if you have a bit of a lead.. you can just control the farm and slowly snowball out of control.. there's nothing the enemy can do about it and the more kills you get in your own lane, the less worthwhile it is to keep trying to secure kills because you put yourself at risk of giving up bonuses.. so instead of continuing to force action, you just take your lead.. group up and objective dance or keep farming until the snowball gets rolling.

Am I missing something? Where's the incentive for action?