Since when did insurance companies become doctor advisors? That's very alarming.If you want to, you can make this sound sinister. But it's pretty common, and the reason behind it is simple.
Many people who need medical care do not see a single doctor for all of their needs. They have a primary doctor, but also see one or more specialists, perhaps have occasional visits with a nurse, deal with a pharmacist, may sometimes need to go to a clinic that's open on a day they can't get an appointment with their regular primary doctor, etc. etc.
Out of that potentially large pool of providers, how many do you think are automatically and quickly sharing full records with the primary doctor? How many others of them receive that level of records from the primary doctor and from all the other providers? How many of them even know about all the others' existence?
This is a genuine problem, because it means that none of them see the full picture of the patient's health. They see isolated bits and pieces of it. And that's dangerous. Pharmacists get a reputation as the last line of defense for many people against different doctors -- ignorant of each others' existence -- unknowingly prescribing badly-interacting and possibly fatal combinations of medications to a single patient, for example.
In the US system (and this is not an endorsement of it), there is exactly one entity that sees everything: the payer (i.e., insurance). All of those providers want to get paid for their services, so every one of them submits claims to the payer, including details of diagnoses, procedures, and so on.
Given this status as the only entity which actually sees the whole picture, it makes a lot of sense to be sharing that information with the medical providers who see the patient. This is part of the original idea behind the HMO model of health insurance (where all the providers are a single super-entity coordinating with each other), though it comes with the widely-hated downside of being unable to see a doctor who isn't part of the HMO. And for many years, even PPO-model insurance plans have introduced more and more active collaboration with providers.