From #28704:

The small size was a request from the git infrastructure team to discourage catastrophic growth of git histories in repos.

Instead of 100KB change limit, what about an over time rate limit. e.g. up to 1MB of changes over an hour. Then tasks that run infrequently can use the feature to save non-trival data. And a burst of activity, which pushes the usage over 100KB, doesn't break a workflow.