Do you know why this is the case? Is there some flaw in their methodology?
If you are done with the "undergrad level" of Popper and Kuhn it is worth reading Imre Lakatos's work on philosophy of science. It contains a moment where one realizes that research programs live or die by this "impact factor" and that this living or dying is a key part of the overall methodology of science. The gist is that science is actually participating in a survival-of-the-fittest evolution with certain foundational ideas as the "genes" which "reproduce". So scientific ideas are actually good or bad in no small part due to their ability to create further scientific research along similar lines. A low impact-factor therefore directly says "along this particularly important-to-science axis, this journal sucks."
Yes impact factor matters to current science as practiced but there is plenty of good criticism to show (at least as it is currently calculated) that it is a lousy measure of what is likely to end up being true, reproducible and useful.
If I read every PoS article vaguely related to my research, I'd never get anything done. In practice, I don't pay attention to impact factor. But I do pay attention to who's publishing. And that's basically the same as impact factor, in practice.
> that it is a lousy measure of what is likely to end up being true, reproducible and useful.
I don't think so.
High impact factor publications are MUCH more likely to be quality science than low impact factor publications (at least in my area).
The major venues would have to get at least two orders of magnitude worse before they became bad indicators of quality.
Of course, and obviously, that does not entail that all work published in high impact factor journals is high-quality.
I think the fundamental problem is just that you vastly under-estimate the enormous volume of utter crap there is out there.
1. Imre Lakatos and maturity are great, both implying that you should not apply the aforementioned rule of thumb to an individual paper - an individual in the population - whether it was published in Nature or an insignificant contender.
2. Your memetic approach is also good, but incomplete: the objective function in case of these journals is maximizing the impact factor - so we can conclude that "PrevMed is less successful in maximizing the impact factor than some competitors, or it is a younger journal, or ..." Yes, imact factor and quality correlate in the long run, but we are not at undergrad level.
3. "A low impact-factor ... directly says" - Not directly. Also, most of the journals - not to mention conferences - do not even have an impact factor.
4. "...this journal sucks" - Most of the people writing in these kind of journals have given up a lot to contribute something modest. The editor of this journal is probably emailing with reviewers at 1am or so. Just saying...