Pension funds manage large sums of money - decent chunks go into indexes but they also have strong reasons to buy stocks.
For example, many funds are based on (i.e. need in order to meet their obligations) ~7% annualised returns. They should and would be in bonds (super 'low risk') if the returns there weren't so pathetic due to prolonged super-low interest rates - the 2008 recovery was made possible by screwing over savers (and in turn pension funds). They have been having to chase equities and indexes can't reliably return the 7%+ they need. Of course, they could lower their returns expectations but that would mean contributions need to increase or benefits need to be cut - neither of which goes down well and becomes a political problem with voters.
In short, they are damned if they do and damned if they don't
The reason why worry kills more people than work is that more people worry than work.