Not 100% sure of the rationale in this case. I imagine it might have to do with everyone who runs an instance needs to maintain an additional storage system along with all the associated costs, which is not just storage alone.
Databases store stuff really well. If get to the level of needing to configure storage for different tiers of access they can do that, it just takes a bit of work. Of course if your blob data is stored in tables that have OLTP data in them, then you have a bit of work to do to separate it out.
This is speaking from recent experience of having to manage random blobs of sensitive data in s3 buckets that engineers have created rather than bothering to put in the main application data store.
I think if you rephrase it that they "dragged the whole company out of the particular IT hell that is associated with banks owning, running and procuring infrastructure" it probably makes more sense.