AWS going down means I've lost it or temporarily lost access to it? Those are two very different scenarios. Of course S3 could lose data - a quick Google search shows it has happened to at least one account. My guess is it is rare enough that it seems like a reasonable decision to not prioritize backing up your S3 data. I'm not syaing "never ever backup S3 data" only that it seems reasonable to argue it's not the most important thing our team should be working on at this moment.

I have my family photos on a RAIDed NAS. It took me years to get that setup simply because there were higher priority things in my life. I never once thought "ahh I don't need backups of our data" I just had more important things to do.