That's also why they publish only a couple of stories per day instead of hundreds, why they never cover breaking news, why there's a donate button (as opposed to now-standard paywalls), why there's no ads, why the interface appears cleaner etc. If we were talking about tech companies, it'd be like comparing Wikimedia/Mozilla/Internet Archive to traditional for-profit tech companies. To an untrained eye there is no difference, but a somewhat trained eye quickly realises that their incentives are completely different.
(Disclaimer: I work for a different non-profit investigative journalism organization.)