Man I figure if you afk for more than 2 games straight, you are intentionally tanking your rank.
Also, what kind of pie chart is this? 42% is like over 86%. According to the text, only 9% are in "consistent AFK behaviour" but the tier 3+ percentage is 24%
Update: these are the correct values provided by RiotAether. In case you want to see the wrong numbers, here is what it was before.