whoever owns it, someone expects you to have it

Being responsible for one's website is our responsibility.  Along with a range of useful and gimicky tools, Blackboard has improved the tool that lets instructors back up their courses.  Not only can you export (not taking some parts of student work -- useful for porting a class to the next semester) and archive (taking the whole thing), instructors can fine tune the archiving, deciding which parts of the course to include.  Once you begin the archiving/exporting, Bb-Learn dutifully performs the function in the background and emails a notice when it is done.  The instructor simply returns to the tool's page and downloads the zip archive.  (There's little point in doing the backup and then leaving it only on the Bb site)

Yes, we could rely on IT's help in rebuilding a course.  I don't know the wait time for that sort of trouble ticket.  And I don't want to find out.  I'd much rather rely on my own backup.

When I am teaching a course, I routinely perform a backup every couple days -- at least once a week.  In between, I always download and save all student submissions.  I avoid using the gradebook for anything more than a way to notify students of their running point totals.  The data exists and is manipulated on my PC using Excel.  So worst case -- the system crashes and we revert to a 2 week old backup.  I'd see what was missing in terms of files and upload them from my computer.  And I'd automatically rebuild the gradebook from the Excel files as I do anyway.

Students don't want to hear excuses about how you lost their grades ... and you don't want to face a Learn-meltdown, especially in the last weeks of a course.

I should add that the worst I've heard of (and it was years ago) was that a patch to the system failed and IT had to bring down the system and run the backup from right before the patch was applied.  These days, we often lag behind the Learn patches because IT uses test systems for almost everything.  By the time we see a patch, it has succeeded on the test machines.  That doesn't help when Bb itself has bugs, but most often, it doesn't cause data loss -- just loss of functionality -- which Bb seldom admits to!

In any case, an important part of using Internet tools is making sure they are stable and you can restore student grades if there are problems.  As instructors we can't rely on or blame others if we don't keep backups.