Could also be incompetence in regards to managing servers and load testing with laziness for not shutting down instances and ignorance of using reserved instances?
Hehe! You will be surprised how often this happens in best of the companies.
A large fintech startup I work with had 5 GPU servers lying around idle before the CTO realized that they only need them while training the Machine Learning models and not during inference stage.
Been there. Remember getting a call from a data center I'd never heard of asking to speak to the old sysadmin who'd quit 18 month ago. They asked something about the rack of servers we had in their data center, I replied "what rack? what data center?" Turns out that 2-3 years previous the old sysadmin had set up a dozen servers in their data center for some project (that I'd never heard of) that very shortly afterwards first got pushed forwards and then canceled. Everybody involved in that project promptly moved on to other things and no remembered to cancel the deal with the data center. So for two years we'd been paying quite a lot of money to keep a completely idle rack of pretty expensive servers and apparently no one noticed.
Ahem, I mean it could be.