Reasons as to why some brands may receive preferential treatment:
- Margins: Some brands/products result in higher profits when sold. Recommending gear that may be better for the customer but worse for the store is something very, very few stores did in the past. Usually, there are guidelines which products/brands to push.
- Advertising: Some companies have budgets for sponsoring articles, etc. It would be unwise to put them off by hard hitting reviews.
- Secondary Sales: Replacing a DSLR with a MILC will inevitably result in some legacy glass being replaced by new native MILC glass. Recommendations to stick to existing technology are hence less likely to be encountered.
- Popularity: Generating a lot of turnover will result in better mass purchasing conditions. This incentivises pushing popular brands and saving critical scrutiny for niche players.
- Courtship: Big brands organise fancy events and fly in "reviewers" to nice locations, pamper them, and provide them early access to new models. Typically, the "reviewers" don't want to lose such privileges. I understand it is furthermore possible that some reviewing gear is offered on the basis of an "indefinite loan".
I don't think that DPRview is Amazon's puppet. I don't think that the DPReview "reviewers" consciously aim to optimise some or all of the above.
It rather appears that DPReview's staff is naturally besotted with mirrorless technology and is genuinely blind to the fact that other users have different priorities. What they are doing works for Amazon which is why the website keeps going.
Should they ever start hurting Amazon -- e.g., by telling people that they don't need the latest and greatest, that their existing gear is fast and good enough -- I don't see why Amazon would continue to entertain an operation whose staff costs alone (apparently there are currently 17 staff members) must be significant, if it does not raises Amazon's bottom line. That in turn, may actually influence DPReview staff more than they care to admit to themselves. The idea that Amazon just runs a website with that many members of staff out of a philanthropic motivation, seems too naive to warrant merit.