Why are beginners always the toxic once?

Ever since the leveling system has come out, I have noticed that those players who are around lvl 30-60 and doesn't have mastery 6 champions yet are always the most toxic of our community. I know this isn't much of a topic, but I find it rather weird how the beginners are the toxic players rather than those in high elo who should get flamed after just a tiny mistake. I'm assuming it has something to do with twitch streamers. But That's my only guess.
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