This is because iPhone photos are ubiquitous which causes photos from less common phones to stand out. And the less common phones likely optimize for this A/B test scenario by e.g. increasing contrast and saturation. Meanwhile Apple likely has little to no interest in optimizing for A/B tests with minor smartphone players, and instead optimizes merely for delivering satisfying photos in the widest range of scenarios.

Pixel photos are very good too, for the record. I just think the "blind camera test" is worthless.

That's quite an interesting way to explain why Apple does poorly in blind tests. The real reason though is that Apple's cameras are just not as good, but I suppose it's easier to explain away by making up biases.