The question is unclear, but let me try to answer anyway.
You assume that for any given field of science, there exist journals with high impact factors. This ignores the specifics of individual fields. In very basic sciences, impact factors are usually high, because many researchers from other fields will use the findings in their own for. For example a researcher from the field of neurology will be cited from the people from neurology, psychology, psychiatric medicine, artificial intelligence, computer science.
On the other hand, more niche the field becomes, smaller is the pool of the scientists that could use the results. While a computer scientist may cite the paper from neurology to reference certain brain structure that inspired his algorithm or massive processing cluster architecture, there is basically no way that the neurology scientist would cite the aforementioned computer scientist.
That's why there are huge differences among fields regarding the impact factor of the top journals in the category.
Does this mean that the paper on some novel computing architecture is less valuable? Certainly not. While very few computer engineers working in R&D of new commercial computer systems will be interested in neurology, quite a few of them will read the paper on novel, more efficient architecture of massive computer clustering.
However, since they are end-users, their reads will not transform in citations, while significant proportion people that read advanced neurology paper will publish papers on their own and perhaps eventually cite it somewhere (because they are scientists, in that essence, not end users).