Why? A new framework gets you new bugs instead of the old ones, but not necessarily fewer or less severe ones.

It’s more likely that things will be reversed: the old, battle-tested framework may have bugs, but it’s is less likely to have serious ones.

They should try to hunt down bugs in the existing code. A partial rewrite of parts that historically have many bugs may be in order, but a complete replacement? Unlikely to be an improvement.

Well I'd imagine the new framework wouldn't rewrite old but wrap the existing low level APIs in a way that is not error prone. Centralize the tricky bits so Photos and third party apps don’t each have to reinvent them?