Programs issue too many miles. There aren’t enough award seats, especially with planes flying full. They need to either increase the number of award seats or increase the cost of each seat, otherwise you just have frustrated members who can’t redeem.
At the same time programs don’t need to spend as much marketing to fill planes when planes are already full. But that’s an argument for reduced earning, not for changing redemption prices.
Programs with set award prices (award charts) usually devalue in a predictable way.