honestly a distributed ledger makes alot of sense for backups, having a swarm of backup nodes which replicate your backup data... good resiliency and geographic distribution.
99.999% of the time what people imagine when they say blockchain is good is effectively just the matrix protocol, which can be summarized as federated eventually consistent databases (and that's pretty dang neato).
It makes no sense at all to distribute the backup generation step, and what do you do with your ledger once the retention period ends?
There may be something you can do with a ledger in the "full - incremental - incremental - incremental ..." cycle, but I can't think of anything that's actually useful.