Tell me why players like this aren't banned

Supports like a Diana that I had today (of all the days, when there are real support champs for free for a month), who refused to take exhaust for their Jhin but ofc got ignite and 'pwomised' not to ks. They also had all ap, 0 gold items, 0 ward items, 0 support items of any sort and not to mention a high number of deaths, like double or triple of all the other team mates... This is not the first time and surely not the last because whenever I report stuff like this as int'ing, nothing happens! Norms or ranked. Rito pls!