Not the same person, but this affects me and I can explain. I have around a hundred apps installed, and use them just frequently enough to keep them around. All of them can sync their data back to a new device without issue.

The problem is that when a new or wiped device installs those apps again, they won't have any of their account or configuration data. Even with a password manager to help, logging back in and configuring my preferences is a tedious, all-day affair. In years past, there were ways to transfer account data, but they stopped working a long time ago. I am eager to find a solution to this that works without root and on modern Android.