Well I figure the opponent can't count on always getting a call later on every after making his hand, because your not going to bet 1/2 the pot all the time with a hand. Some might just be ace high continuation bets or marginal hands where your opponent doesn't have implied odds.

In the better scenario for example you bet $1 into a $2 pot on the turn. He needs 1:4.9 pot odds. So he needs $1.9 in your future bets. He calls and makes his hand. Pot is now $4. He needs to bet more than 1/2 the pot and get a call and win to make a profit on that decision on the river.

Flush would be $1.2. That's less than 1/3 the pot on the river. It's easier to spot a flush on the board. But I see your point.