Amazon has 150,000 employees. Granted most of those aren't in IT, but it's a pretty big place. Take a look at all the services they provide, and think about what it takes to deploy and support them. Their cloud computing As-A-Service effort offers load balancers, SQL clusters, VMs, archive/backup storage, DNS, network topologies, AV transcoding, Hadoop, machine learning, etc. Each of those paid offerings has a develop, test, deploy and maintain effort associated with it, as well as effort to maintain the authentication & authorization components, and provide consistent user interfaces across technology designed by a plethora of vendors.

When you factor in management overhead and unreleased products, it seems like a few thousand is reasonable.