Once a managed provider steps in, they want to "own" the configuration. You end up with the operator itself actually having to raise tickets with the MSP to change things on their own network.
All this becomes a huge issue if there's a major outage, as the MSP might not have enough access to actually get in and do anything.
Most telecoms networks are run (to some significant extent) by a managed service provider, in my experience. When O2 UK had a major core outage due to an Ericsson certificate expiry inside the core, it wasn't O2 engineers that found and fixed the issue; it was Ericsson engineers.
The margins as an operator don't make it easy to keep around the deep technical skills to be an expert in the network you own.