Monorepo monoliths make it hard to experiment. Getting something as benine as a later version of .NET becomes a mammoth task requiring the architecture team and everything stays old. Want to use a reasonable tool? No chance.
A monolith that's broken up into 20 libraries in their own repos also prevents experimentation with new runtimes just as much as the monorepo version does.
Monorepo also means a team 'vetting' new thirdparty libs, and a team telling you your CI takes too long, and a team telling you to upgrade your lib within 23 minutes because theres a security issue in the korean language support...
It sounds like you worked in a dysfunctional organization that happened to use a monorepo. Their dysfunctions are not inherent in the monorepo model and they would have found other ways to be dysfunctional if not those.