That's an incorrect assumption on your part. DDG allows you to execute search queries without associating those queries or results with any of your personally identifiable information or accounts. Its claim is to provide private search. No part of their mission claims to never use "Big Tech" companies for infrastructure, transport, etc.
Again I'll come back to my example. Do you think that SNHU being hosted on Azure means Microsoft just gets free access to all of their grades, research data, user/student/faculty information, PII, logs, to use for their own business purposes? If that's what you believe is happening, then this applies to every company who uses any public cloud provider.
Seriously, I'd love more proof or sources for these claims that Microsoft (or any company) is using its position as a cloud provider to harvest information from private companies. Otherwise it's nothing more than a conspiracy theory driven by traceroute output, thrown together with misinformed news articles about business contracts.