Agreed, but you don’t want keyboard accessible menu items available for users that aren’t visually impaired. Offering a “show menu” button to screen readers is not less accessible to them than skipping the navigation section.
If you’re building a page that is only meant to be used by screen readers, then you are absolutely right.
> Meanwhile, non screen reader users are forced to guess what will be behind the ≡ button this time.
The main menu? Which is behind the same ≡ button on most pages on the internet?