The block reward is a node incentivization.
The block reward is an incentive to contribute hash power. Running a node is secondary to this and an after thought for many, or not even a consideration for some. Lots of people (maybe the majority of miners?) buy an asic miner and connect it to a pool and don't run their own node but still get block rewards.
I am guessing that the majority of the nodes on the network are actually getting no block rewards at all and get no direct rewards, but instead are there because people want their own node to make transactions from, or they own a lot of Bitcoin and want to protect their investment so they contribute to the network.