Without knowing more about their architecture it is difficult to comment beyond the conclusion Alexandra Noonan came to, stated at the beginning of the article. It looks like to me that the architectural assumptions were changing too quickly due to the demands of a fast growing business. Having all their code in a single repository means that they can control dependencies, versioning and deployment centrally, it gives them central control of their software development lifecycle. I can't see how they could not have had the same benefits of the monolith if their microservices existed in a single repo to begin with and had the appropriate tooling to enforce testing, versioning, deployment across all services in the repo. I guess this is the whole monorepo debate and tooling.
This article for me is more about the complexity of managing a large team across different sites where the architecture needs to change rapidly when modularity is absent. They did get a measurable benefit around performance, though. I wonder if Alexandra will comment on the challenges of running a team in an environment of this complexity?