The lead for a project I wasn't working on casually informed me they were doing this a few years ago, the reason for it was nothing complicated, they just hated HTTP status codes and believed it was easier to pretend they didn't exist.

I mentioned that it was frustrating to work with APIs like that since a bunch of tooling relies on status codes, including the browser network tab but they just told me they didn't care. They also made a bunch of other questionable design decisions before leaving, so now I just take it for was it is, a red flag.