The divergence in AIG occurred to a large extent in 2010. However, this effect is present for most stocks and the indices as well and has existed for pretty much as long as we have reliable data without survivorship and lookahead bias.

Is it surprising to you that the effect was larger for AIG around 2010? As AIG was going bankrupt and the common stock holders were effectively getting wiped out, individuals were willing to hold AIG during the day to play crazy intra-day volatility but unwilling to hold AIG overnight because most announcements around restructuring were happening overnight.

Of course at the time short sales on a list of stocks including AIG were forbidden. So even if you ignore the fact that most day traders etc prefer to play things on the long side, you have the issue that they couldn't play the short side even if they wanted to.