Its not just the scientists. Laboratories are judged (and to some extent funded) based on the total impact of their publications. You get there with a few easy steps:
1) public decides that funding science is good
2). lots of organizations compete for limited funding
3). Public needs to decide how to allocate funding and needs a metric for measuring the performance of these organizations
4) Public decides that peer review is a good metric
5) Important publications are sent to the journals that have other important publications, those that are rejected go to lower level journals. This establishes a hierarchy of journals.
6). The public considers publishing in higher "impact" journals as representing more value.
It is all logical, and a difficult system to fix. If I have a really good publication, I am hurting my career and my laboratory and coworkers by not publishing it in one of the premier journals. I'm even hurting science because by publishing in a lower impact journal, my (presumed brilliant and important) publication will be read by fewer scientists.
As an aside, a lot of the published material is also available to the public for free (all my stuff is also in SLAC pubs as is required by DOE), but these do not rate as high on a google search so you will have a more difficult time finding them. Google, like everyone else, gives higher ratings to the prestigious journals.
I wish I knew how to fix this. It is quite frustrating that 3rd party companies are paid for my work. To add insult to injury, I often review papers for these journals - and am not paid for the reviews. I could turn down the review requests, but peer review IS a vital part of science.
To the previous poster - the problem with non-anonymous reviews is the risk of "trading" good reviews, retaliation etc if the reviewers are known. Scientists are people, as easily tempted to misbehavior as any other group.