Global Financial Crisis was a big turnaround for most of the so called developed/developing economies in general and practically almost all their stock markets in particular. The impact (mostly negative) was so huge that it needed several years for many companies to recover and get back in the growth trajectory. It is also learned that many companies had to close down as they couldn't recover the impacts. GFC was without doubt a black swan event which took most economies on a tailspin at least for a few years. So any study that compares components across pre GFC and post GFC periods are clearly justified in their approach.
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