It might seem like a trivial detail, but it's not for people who depend on keyboard navigation nor is it for any form where users might want to keep the button focused after submit. You don't have to use a screen reader to be inconvenienced here.
I've had to handle the latter case in game-related apps, but another example off the top of my head would be the obvious ability to resubmit the Reddit reply form by hitting Enter again when it responds with its "Error, try again" message. I don't see the argument for settling for the poor UX of using the disabled attribute here if you knew better and had the time/energy to polish it.
There is a level of polish where it makes sense to replace the disabled attribute with a disabled (e.g. "submitting") class which implements all the things you expect, like pointer-event changes, but is even more powerful, like being able to use it on a wider variety of elements and even container elements like `form`.
Finally, as the article points out, you still to write JS to prevent double submits even when using the disabled attribute. It's used as a quick hack rather than any sort of "submitting" semantics, so there's nothing lost recreating it with CSS.