I worked at a company that went through this transition from thousands of microrepos to a monorepo. The main driver was application security. When everybody did

I worked at a company that went through this transition from thousands of microrepos to a monorepo. The main driver was application security. When everybody did their own thing in their own repo, rolling a new version of a library with a critical security fix was very expensive. It was impossible to complete in a reasonable amount of time, because you'd frequently find legacy services that were on some previous major version that required rewriting code or upgrading other libraries to implement the fix. A monorepo means every service is on the same set of versions of every dependency at a given point in time. It's much easier to reason about what is fixed, and move everything to a known good version.