In this case it was shiny object syndrome on the part of a few early architects.
The whole project could have been a Rails app.
The lesson is less about event sourcing, and more about picking architectures in light of business needs rather than trying to be fancy.
However it's silly IMO to use that criteria as an example of why not to do event driven architecture. It's well understood in the eda community that you generally don't start with streaming systems unless you know you need it from the start.