Steemonsters doesn't work with upvotes, the value of DEC is actually backed up by what can be bought with it (cards, potions packs, ...). The only way to earn DEC is by playing the game which actually is an enjoyable experience like many games people play and actually pay for. The better you are at the game which is also directly linked with the value of someone's collection, the more Dec you can potentially earn.

There is no post2mine / upvote4upvote / pretend2care / Abuse bullshit when it comes down to Steemmonsters unlike pretty much every tribe or dapp like appics/sportstalk that work with an upvote reward pool system. DEC is pretty much the only steem-engine coin that managed to increase in value as the game got more users the past 20 weeks.

Of course the price goes hand in hand with the game popularity and it's inevitable that one day all cards and DEC will be as good a worthless. The life cycle is just way longer than the existing tribes where people just bought coins to earn more coins which quickly dried up.