Those batteries are glued in to their own rigid case, which makes swapping them out of the laptop trivial but also didn't leave much room for expansion inside the battery pack, and the battery pack was pretty thick compared to any recent Apple laptop.
Replacing the cells inside one of those packs would have been similarly difficult to ungluing and replacing the batteries in more recent Apple laptops, but there was a lot less reason to rebuild those battery packs.
Replacing the cells inside one of those packs would have been similarly difficult to ungluing and replacing the batteries in more recent Apple laptops, but there was a lot less reason to rebuild those battery packs.