1. The "Bus Factor" - https://en.wikipedia.org/wiki/Bus_factor
2. Context switching - if you have a developer that also works on coding or other things.
So maybe it's not a full $240k/year for only 1 service, but the price in the door IS that. 2 to 3 extra services will cost no more - that's where AWS will make the money.
At scale, the arguments about needing 10 admins vs needing 15, for example, start making sense.