One possible view is that a company grows to the point where it goes from being a recipient of investment, to a source of investment. Also, the managers get too far removed from innovation, to directly engage in or direct it.

I work for a F500. The top brass of the company sincerely want us to move into new areas. So they just buy companies that are already innovating.

People recognize the problem of big companies trying to innovate. One solution is to create isolated innovation teams that function more like smaller companies. I work in one of those teams.