While this definitely used to be the case (we used to find ~80% of incidents were internal employee issues), for the past four or five years we've seen that ratio change (not so much because the internal issues went down, but more because of the rise of external activity).

The reality is that organizations have to be able to deal with both internal and external threats, and a lot of the effort on that front has been around reclassifying access to no longer consider insiders as trusted (which an argument could be made that they never should have been trusted to begin with).