You can see [1] that they are using multiple cells essentially taped together to make their "battery". This isn't uncommon, especially recently in smaller devices, as it lets them fit unusual shapes and other size issues, and saves space because you don't need a shell around them. The biggest (only?) issue is that you have a very delicate batteries taped together, if ripped/torn they may explode. To add to this, because they aren't riggedly attached, they are more prone to movement (and thus tearing). Their solution was to use adhesive across the bottom to make sure they are all firmly in place [0].
From a repair perspective this isn't great. It's not hard to remove if you have a heated plate, isopropyl, and patience, but not very user friendly. The best thing they could do to fix this would be to give the battery a rigid enclosure, but that will of course eat up valuable space, and I have no idea how that would affect the rest of their design. They could also use different tape that's easier to remove, but they may see the taped-together battery as something they don't want to be liable for people replacing (in case they tear it), so I really think the best solution is a rigid shell for the batteries.
tldr; This appears to mostly be a design limitation instead of a purposeful decision. I wish they'd change their design instead though....
[0] https://guide-images.cdn.ifixit.com/igi/FkZHQOAv2sPqKSBE.med...
[1] https://guide-images.cdn.ifixit.com/igi/VJBBLeHLWsRBQeIS.med...