However, I don't understand why review sites don't simply contact the producers and ask "when did you start? Much of the information needed for a "meaningful" evaluation of a site can unfortunately not be found on the internet and is publicly available.
Because most of them are lazy slackers who don't care about the accuracy of the information they publish, but only about getting hits to their blogs and making money from affiliate links. They write so-called "reviews", which is all a load of crap, to get more referrals, but not the proper type of reviews that have real value. And this kind of attention whore behavior is going to get bigger and bigger, since it's easy and cheap to generate these kinds of information dumps and therefore it's attracting more and more people.