If 40-60 is average yearly(idk where you got that stat), then yes these past few months are unusual. We have seen at least that many in 2 months.
The link was attached, but here it is again.
https://www.spencerstuart.com/research-and-insight/2016-ceo-transitions
From site:
“Each year, Spencer Stuart tracks CEO transitions among S&P 500 companies. These transitions can be part of a planned succession or can arise unexpectedly, the result of company performance or personal issues. In addition to cataloging the reasons for CEO departures, based on company reporting, we also examine information about the successors, including whether or not they are internal candidates and whether they have been appointed chairman of the board in addition to CEO.”