1. Nodes can be sybil attacked, there is no cost so there cannot be an objective way to reward them nor any true measure as to whether they are doing any good for the network.

2. Running a node is more a defensive measure than an outward service. Kind of like holding your own keys. Nobody should be rewarded for that, its just dumb not to do it. However if everyone holds their own keys the network is stronger for it, similar with nodes.

3. Nodes and miners weren't separate ideas in Satoshi's time. There was simply the Bitcoin software. If you installed it, you were a full node and a miner. It wasn't for a couple of years before mining was so pointless on non-specialized hardware that node running became a separate idea from mining.