Possibly because nobody has ever reported it as an Issue, that I can tell. That’s the first step in getting a developer on it – and there are far too few developer volunteers (910 issues currently in Issues backlog). Even after getting a volunteer, there’s still a learning curve. Nobody instantly knows the entire code base.
If you’re a skilled developer, pull requests to improve Duplicati are sought. That’s how progress happens.
There are also far too few forum volunteers, and that keeps some potential developers tied up on forum.
This particular issue is arguably user entry issue, but the documentation and UI don’t help users enough. The GUI might be able to warn, but not everything is GUI. Duplicati also runs from the OS command line.
Another design issue is whether the issue should just be silently fixed by changing backslash to forward.
Problem there is that backslash is a legitimate character for a path on some systems, but not Windows.
Duplicati now offers 28 options on its Storage Type dropdown for Destination. Each one may differ…
expresses the problem of too many storage types, so it’s hard to even document it on Storage Providers.
One might say each particular storage should error gracefully, but again one gets into how to even test it.
Possibly a generic solution can be found, but it’s still a research effort that some developer must take on.
What remote storage is yours? Feel free to file or find an issue with all the steps to reproduce your issue. Proposing a specific solution that is reasonable to implement (given the above) would also be valuable…