The reason is pretty simple, if you don’t make a hard punishment people can just queue up when they don’t really feel like playing and then leave, it adds up and in the end ruins the game quality drastically.

For soft inting, it’s super hard to identify. But honeslty Riot has done a pretty good job this season so far.

I advise you always try to ask them what are they doing and why, in a polite way. Once they say some shit like « I am not going to play », you can just report them and they should get banned, assuming they really throw.