What next? Create their own Binary Flag (0/1) scheme?
A huge company the size of Amazon should have a small internal team of Database Professionals to invent and manage their database concepts, structures, and lowest level software. It's just not that complicated to create efficient and scaleable data structures. You don't need outside help, unless it's clearly better faster cheaper.
Using outside DB software has to be demonstrably better, and provide better return. That's unlikely given the scale of Amazon.
Whoever has been signing off the invoices all these years should have noticed.