The reason you always expect growth is because as a company retains earnings its total assets grow. You expect that given more money you should earn more money.

The reason you always expect growth is because as a company retains earnings its total assets grow. You expect that given more money you should earn more money. If you get to a point where you're earning the same amount but require more assets to do so, you are going to get a lower multiple on your earnings. The other option is to payout all your earnings as dividends but the problem there is double taxation(if you live in a country that taxes dividends) which lowers the value of those earnings to the investor.