Why does the disabled check for custom web components require formAssociated?

[richard-smith-preservica]

This is an explicit decision, in utils/misc/isDisabled:

      if (
        (el.constructor as {formAssociated?: boolean}).formAssociated &&  // <-------
        el.hasAttribute('disabled')
      ) {
        return true
      }
    }

We have web components that support disabled state, but userEvent.click was still 'clicking' on them when disabled, even though real browser interaction wasn't (because the elements inside it were also disabled). This was resulting in a test incorrectly failing because it 'clicked' on disabled elements and performed actions that were not actually available in the UI.

My question is: why is an element exposing a "disabled" attribute not a good enough indicator that it should be considered disabled from the perspective of tests?