I get why they might be doing it ( audience building ), but they should have restricted it only to their HomePage or some info pages. ( check azernik's response on how to do this correctly ! )

It's easy to attack Backblaze.

Before attacking them for this, please make sure the company that you are working for or building doesn't do the same thing. ( I know for a fact that a lot of startups make heavy use of Audience building).

Note : I have used their service in the past and moved on to OVH due to a different issue in the past . https://www.backblaze.com/blog/b2-503-500-server-error/