It makes perfect sense because just like every other cloud company, they hook you pre-IPO. Post IPO or buyout, with lots of customers dependent upon them, they can raise their prices to a bit above market price because their customers will resist moving.
Think about it: if you have a backups stored with them via their proprietary backup client, you have to stick with them or lose all your backup revisions; there's no way to move revision history.
That's why they charged below their own rates, they knew people would be trapped.
Backblaze backup plan pricing is about to skyrocket.