Selling 20 millions would cost you a little fortune in broker fees. In turn BRK are buying back and paying brokerage. It makes sense to sell directly. And I don't think you get a better price than the market even selling 20M, you just sell at market price.
This saves money to YOU, the shareholder, so you should be happy with it.
Broker fees? I assume you mean the individuals entity that manages their portfolio charges a fee. Obviously when you have that much wealth you aren’t using E*Trade or Schwab $0 commissions trades.
This saves money to YOU, the shareholder, so you should be happy with it.