Decred should be mined by people who deliberately want to participate in PoW for profit, not just dump it as a byproduct of a primary coin.
I am not sure if it can be changed, but it would be advisable.
I don't really see the issue. Those people mining are still spending their money for electricity and putting wear and tear on their hardware to mine DCR, it's not just falling from the sky into their laps for free. Now they have worked to acquire DCR and from that point they can decide to keep it if they believe in it or sell it off like any other crypto. The market decides what something is worth and apparently people don't care that much about DCR and are selling it. It is what it is.