Horace Dediu does some digging:

But besides this interesting history lesson, there is a deeper, unsettling observation. The scale of these periods of prosperity is far shorter than the average person’s career. Indeed, the entire time span of the study is 35 years, about the time an average person will be employed. All the companies failed to maintain prosperity over this time frame.

The implications for company managers and workers is profound. Chances are that the business you work for will not prosper for more than a decade and will reward you for an even shorter period. Similarly, as witnessed by the P/E ratios, investors have given up on this industry as one with any quality of earnings.

There is no “rule” that this has to be so. The high mortality rate and short longevity of technology companies is a consequence of a failure to manage innovation and disruption.

Maybe the fact that people don’t work for the same company their whole lives anymore (like “our parents”) is a chicken or egg problem. The pace of disruptive change is just too fast for anyone to stick around at one company their whole career anymore.