The incentives aren't there (in my opinion) because the average person doesn't actually want to see that level of info. They're reading (or more likely, skimming) these sorts of reviews to have someone tell them what they should buy. The reviewer could go into a crazy amount of detail to figure out all of the thermal characteristics of the thing they're reviewing, but in the end it won't make a lick of difference compared to doing "just enough" and recommending something "good enough." Especially when, in most cases, coolers on the market these days are either "good enough or better" or "junk" and it's not hard to tell them apart.

There are exceptions to the above, like GamersNexus, who do take a slightly more scientific approach to things, but at the end of the day, most people don't care.