Pete, defined benefit schemes closed because companies and individuals could no longer fund the hugely costly benefits they promised. The costs were huge because we moved into a low interest rate environment causing Gilt yields to fall (universally seen as a positive) and much higher life expectancy than previously expected by actuaries.
Alternatively, of course, companies could have asked shareholders to stump up the cash to fix the gaping hole on their balance sheets caused by unfunded pension promises, thereby reducing equity prices and capital for future investment. I think not!