Man, this is a frustrating and shallow criticism. Obviously this is over-engineered. It's a demonstration of how these patterns would fit together in an application that required them.
You're right they could have... beefed up the soda can, so to speak, but I don't blame the (presumably) DevRel folks who put this together for hand-waving it, "now imagine a mountain here".
I would very much agree with that. Although I'm not against microservices, they are by no means a quick or efficient way to get things done. Hedging against future theoretical scaling concerns comes at a high cost - a cost that's very much worth it if true scale is achieved, but a high cost nonetheless.