5000 seems to be a nice sweet spot for the amount of usage bitcoin is getting. If it went lower it would be a problem and big blockers want to lower the node count while raising the usage.

Oh and dont forget, it's not only about node count. If a big company fills a building with nodes, that counts a single point of failure, so it's useless to strengthen the network. Nodes must be spread all over the place by individuals, any other models are weak, hence why conservative blocksize is a reasonable tradeoff.