In concerns of how you probably see more toxic players, it may have to do with the player-base the game surround you with. You typed you started ranked, so you probably played with different players compared to me. So, the point was to type that I do not find many players to be "toxic". It may also have to do with our definition of that word and our own perspectives. Also, it's possible emotions are in the way which clouds judgement and most commonly, make people see other players as toxic.
Why are so many people in this game toxic? I don't understand the reason behind it asides from maybe wanting to cover up their own insecurities.
There are plenty of reasons for their toxicity (no reasons excuse their behaviors, nevertheless). It's not always a simple cause such as trying to "cover their own insecurities".
I often see that reasons typed among other areas of discussions, and the USUAL true intention is to patronize those "toxic" people and make the "victims" feel better. Seeing yourself better than others and treating others below you like trash is not a good way to mental/emotional development. It's not always how you solve problems/tensions either.
Condescending others is what toxic players do in the first place. Acting/thinking toxic back at those types of players does not make the "victims" truly better.
Not only that but why do people take this game seriously in the first place?
Plenty of reasons as to why people will find reasons to be angry about. The root of the problem is themselves, but that's not the concern. It's not that it's taken seriously only.
Time, expectation of other players, goals (to reach the higher ranks), can cause anger.
I also wonder why there's no option to turn off chat completely?
The best you have is /muteall. You type that in the chat to mute everyone, I believe.
I think the option is not available because people would lose POTENTIAL communication. If a player wish to spend time in this game, but wish to not communicate with others, that player has to give a small effort in their fingers, and some effort in their brain to type /muteall. It take effort mentally/emotionally because of several reasons such as pride, tendency to retaliate, or anger.
Personally, I never use the mute function as I do not stress, I do not have hatred toward others, and I mostly type to give information. I wouldn't want players with different perspective from me to have an option that preemptively remove that chat. I think an easy access to that function would make more players unnecessarily removing the chat box.
What are your opinions and ideas on the matter?
I never had a personal problem with toxicity. They never bothered me, I do not bother them verbally. I typed "verbally" since sometime my game-play sucks and it may anger other.
My main concern is how the players AROUND me deals with toxicity. In a game with random people, you may have toxicity vs. toxicity. It's not always a simple case of "toxic against a nice person". Not everyone is mentally/emotionally developed, and it shouldn't be expected as such. It's not something Riot can help with unless they have someone to spread the word of wisdom and development that could sway all minds for the better.