That's basically the case with any game, to be honest.
Take Chess, for example. Sure, you can simply hop into a game and move things however you want (so long as you're using legal moves, that is) and possibly win. But, the game isn't just about moving pieces. It's also about knowing what pieces can go where, how each piece moves, what your opponent may do, how you should start your first turn, how you should set up the board, how to manipulate your opponent into moving pieces you want them to move to where you want them to move them, etc.
There is no way for a newcomer to Chess to be able to know all these things, right off the bat, so they have to put the time in to study different strategies, as well as, different opponents' strategies. Most, if not all, Chess players even spend hours a day practicing the game by playing against themselves.
League of Legends is by no means a game that one could simply jump into and carry hard. There are many, many Champions to choose from and learn. And there are also many different items, item builds, mechanics, etc to learn and master as well.
1 or 2 games a day (especially if only every couple of days) is not going to give you enough practice time to learn anything. That's not saying you have to spend hours, upon hours, a day to learn the game. But, playing a couple games every day (or every other day) will teach you more and give you more time to practice and find out new things.
