I don’t think insurance companies provide unlimited coverage for anything, All companies generally have caps and exclusions.
Its hard also to pain the insurance company as the villian. The insurance company didn’t set the drug price at 2.1 million per dose.
If insurance companies did provide coverage without limits, the premiums would be much higher and fewer people would be able to afford the policy. This is an awful situation but premiums were collected with a certain benefit promised and funded.