To somewhat alleviate the issue of bad-actors running multiple nodes, a lottery would also be implemented to distribute reward.
If the lottery is only based on keys, what stop bad actor from run multiple node client with different addresses on single server to increase their chance to win the lottery?
There is ABSOLUTELY no reason there shouldn't be a reward for running a full node to answer the initial question, (just ask your local ISP if they think their bandwidth should be free) but I am not as smart as a hair on gmaxwell 's head, so I'm sure there are lots of flaws in my idea. Which is one of the many reasons Poncoin was never done.
The reality is there's no incentive to reward node/participant on most decentralized/distributed system, while ISP can't be categorized as decentralized/distributed system.