The real problem with the game pace

is that a single mistake can be capitalized on too hard.

For example, you give up a kill bottom lane? Apart from getting gold advantage and getting ahead in XP and getting some tower damage, now you also have priority over the river scuttle. It's now an extra thing to give you an advantage. Riot keeps adding more and more things that people can claim to get bigger leads than necessary.

Other situations are: mid lane, you take an equal / slightly advantageous trade, but you also get to push out the lane. Because of that, now you are able to roam to the river, pick up the honeyfruit and get a big lead in HP and Mana.

Your top laner got a good trade and now has priority? As a jungler, you can now go into the enemy jungle on that side, and pick up the farm, while having the safety to get out because of the blasting plants.

These are all things that aid players to get bigger advantages, given the opportunity, and it's why people get to outpace and snowball that hard. It's one thing to take an enemy tower because of a kill, and another to take FIRST tower, scuttler and the entire enemy jungle safely.