Look, this is just an incorrect oversimplification of the problem. It's popular on the internet but it's just factually incorrect.

Here's a thread discussing the exact problem I'm describing

https://www.reddit.com/r/AV1/comments/1co9sgx/av1_in_dark_scenes/

The issue at play for streaming services is they have a general pipeline for encoding. I mean, it could be described as cheaping out because they don't have enough QA spot checking and special purposing encodes to make sure the quality isn't trash. But it's really not strictly a "not enough bits" problem.