This is true. But there’s another side to it too, which is that if the industry was more profitable it would (probably) attract more investment, specifically in the form of new companies.
That depends what the startup costs look like. If the barriers to entry are low then you don't need a lot of investment to enter the market -- which is one of the things that causes margins to be lower, because otherwise people would keep doing it until the returns fell below the normal market rate of return.
The industries with excessive margins are the ones where the incumbents make it prohibitively expensive for anyone to invest in those industries by entering them as a new business, as opposed to buying the stock of the incumbents. Which is one of the risks to their investors -- their stock prices are thereby inflated and they're running the risk both that voters will never get mad enough to actually push through regulatory reform and that the huge market incentive to find a way to disrupt them will never actually find a way do it.
