An unstated goal (we probably should have stated it, looking back) was for sites to be able to easily move legacy sites with legacy endpoints to long sessions.
The service worker approach can effectively intercept requests to any endpoint and perform the re-generation of a short cookie if needed, without needing to change every page on the site or the legacy endpoints.
One additional benefit is that it minimizes the transmission of the long term token, which is generally good if you're worried about it somehow getting intercepted. You may or may not be too concerned about that risk though.
An unstated goal (we probably should have stated it, looking back) was for sites to be able to easily move legacy sites with legacy endpoints to long sessions.
The service worker approach can effectively intercept requests to any endpoint and perform the re-generation of a short cookie if needed, without needing to change every page on the site or the legacy endpoints.
One additional benefit is that it minimizes the transmission of the long term token, which is generally good if you're worried about it somehow getting intercepted. You may or may not be too concerned about that risk though.