You need these things to run a global operation at scale.
If you're not interested in running a global operation at scale, then you can be happy running a little self-serve application - but to create the phenomenon that is SnapChat requires a lot of coordinated effort. To think otherwise is just simply naive.
Now I don't think we have enough information to judge if 1800 is the wrong number for SnapChat or not. They very well may be overstaffed.