You aren't missing anything. I use B2 along with Restic to backup my Linux machines since their standard backup solution doesn't support Linux. It costs me around $1/month to backup my primary desktop and two laptops.

They had a blog post about doing this a while back, so they are definitely aware of the use case: https://www.backblaze.com/blog/backing-linux-backblaze-b2-du...

I still use their standard backup service for my family's Windows machines since its more "batteries included".