Draft Mode?

I'm here just with a quick question.. Why does draft mode in non-ranked matchmaking keep disappearing on certain time? After im really forced to play few normal games and arams Its back on. But Im sick of this because I hate arguing with people which cant read or are just ignorants in normal pick mode and I never play what I want there. Thx If someone can explain me I dont know if its mine problem or riots or its on purpose like this..