The block reward is calculated based on the last block's difficulty and current network hashrate.
If the network hashrate jumps up a lot during low difficulty then it will result in a low block value.

Some pools and miners are configured that when the difficulty goes up they usually switch over to another coin - leaving a very difficult block for low hashrate to solve

PHC tries to automatically discourage this behavior. When the difficulty is high and hashrate is low - those are the most profitable blocks to solve! Pool jumpers are merely scratching the surface of their potential earnings..