#1. Green light disappears when a new block is generated by a new miner. If you take a look at the bitcoin-NG whitepaper you can see how this would be done with coreblocks only occurring about 10 minutes apart and small blocks generated between them. (I am not involved with Bitcoin-NG at all I am just partially stealing there design). 

#2. Real miners only get fees when they include a transaction into a block. If the block is almost full then the number of transactions they can include is fixed. So they need to maximize the fee per transaction. Thus in the example, because the number of transactions being placed in the core is reduced, the the actual fee/per transaction increases; and thus miners make more money and thus have incentive to do this.