Most reviewers simply can't evaluate products over a sufficiently long term to make convincing judgements about reliability. Where the latter is important, it's better to consult a source like consumer Reports that specializes in that sort of longitudinal assessment at the price of narrow product focus and shallower review detail.
But ultimately, for reviewers, what matters is that they “make a living through reviews,” so they have to say things that fit the fanboy tier they’re targeting.
The problem is that fanboys are generally people who buy more devices to begin with, so they also judge reliability based on the existing product lineup, and reviewers are largely the same. As a result, they can’t help but judge mainly by new features.
To be precise, “reliability” requires predicting the future, and that’s not easy. How would you know if your computer might break tomorrow? There are serious hinge issues with the iPhone Duo right now—how would people buying it have predicted that?
Prediction is basically break-even even when you’re right, and easy to criticize when you’re wrong, so it’s a hard attribute for reviewers to review.