Form tags usually contain other elements - textboxes, checkboxes, etc. The url and method are specified on the form tag and not the button, so if you want a second submit button that goes to a different URL or use a different method, you need to duplicate all the other inputs in a separate form tag with your button.
All of this can be done with scripting, but the point of this proposal is to make that unnecessary.
An extra blank form on the page and the form attribute on the button can work around that, and at that point the argument would basically be: this is super clunky.
you can have the backend at the first URL detect which action should be taken based on which button was pressed, and act accordingly—even up to passing control off entirely to a different route/method.
The proposal has an in-depth explanation of why this and other workarounds (like using the `form` attribute and a bunch of dangling forms) aren't sufficient.[0]
[0] https://triptychproject.org/proposals/button-actions#existin...