Players harassing new/unskilled players

I am a relatively new League player, as I started playing this summer and have been playing for only a few months now. Since I have only been playing a short time, I am not too good at the game yet, but I am most certainly improving. Unfortunately, I often get put in games with people that have much higher skill and experience levels than me, causing me to perform poorly in many games. My teammates often harass me and tell me to "go uninstall the game" due to my poor performance that is caused by an unfair match-up. Why are many players very rude and harass new players? I have observed them harassing other new players and telling them to quit because they suck. I need to play to get better, but so many people are so mean. Why are so many people rude and mean to new and unskilled players? and why do I often get put in games with players much better than me?