I'm having to back up data to re-install/clean-install W10.

Owing to noting how huge File History was....I took some large folders out of the backup. (4GB, 6GB, 7GB)

On re-running the Backup each time, it didn't get smaller, it got larger and larger.

The SP3 is hardly used....77MB music on it.
Plus about 5GB of residual Dropbox folders (left over from what I already cut out). I guess the notorious Outlook backup (3.3GB) is bloating it, but that wouldn't change within an 8-hour period.

I thought it was a smart backup, incremental-like. Anyway, guess not, but why is it getting bigger? It's up to 28GB now.