Because some users don't need reliability beyond what a normal hard drive offers, and they really shouldn't be compelled to pay for it. If you need reliability

Because some users don't need reliability beyond what a normal hard drive offers, and they really shouldn't be compelled to pay for it. If you need reliability on these devices you can run software RAID or ZFS over the raw block devices being offered and tune the cost/reliability equation in whatever manner makes the most sense for your application.