I don’t think your last sentence is congruent with what you were saying before it.
You’re saying a CEO will opt for conglomeration because it either increases the value or decreases the volatility of the company because the CEO has lots of stock in the company. If that’s the case, how is it bad for the shareholders, of which the CEO is a major player?
The Behind the Bastards podcast covered Jack Welch, definitely worth a listen.