Please, grow up.
They don’t. They make a best effort, and they even have vendor support.
There is no incentive for display makers to have up to date or relevant information embedded in the display’s firmware; some vendors copy-paste the EDID data from one model to the other; I’ve seen displays from major manufacturers with physical dimensions set to 16 millimeters by 9 millimeters. There is no validation process for display information.
This is why “hardware lies”: there is no incentive to tell the truth.
In the absence of a source of truth, and because different people like different font rendering results on any platform, we can only punt the decision to the user.