why can a bot dev not just get all of these values from the laptop's settings and hardwire the headless version to have the same values?

Because the expected values are not fixed, it is possible to measure response times and errors to check whether something is in the cache or not, etc.

There are a whole host of tricks relating to rendering and positioning at the edge of the display window and canvas rather than the window, which allow you to detect execution without rendering.

To simulate all this correctly, you end up with a standard browser, standard execution times, full rendering in the background, etc. No one wants to download their YouTube video at 1x speed and wait for the adverts to finish.