I believe one very strong reason is that people are unwilling to follow the intellectual path to their final conclusions. If one is well read enough in the evidence for evolution, one must reject religion entirely. Only atheism or deism remains. There are many people unable to accept that conclusion and thus reject it in some way.
It is the same with global warming. If one reads enough about the evidence, the only conclusion, if nothing is done at once, is that civilization is in most respects doomed. Again there are many people who cannot accept that conclusion, even fewer than who accept evolution.
The really interesting thing though is that denial of either of these issues is very strongly correlated with being politically conservative. The evidence on these issues is widely available to anyone with the sufficient interest in investigating them. The evidence fundamentally has no political dimension to it, so why the strong correlation?
There are people researching this topic:
Social scientists have been investigating this disconnect between the evidence and expert consensus, and public opinion. Is it caused by information deficit and misinformation surplus, political and ideological biases, or some combination of these factors?Apparently to some degree "hierarchists" reject global warming but that doesn't explain it.
In another interesting result, perceived knowledge made hierarchists (those who favor distinct socioeconomic classes – closely related to the ‘religious right’ in the USA) more likely to reject that humans are causing global warming.Attributing this to the "religious right" is incomplete because meterologists, presumably not dominated by the religions right, also are denialists. For these it might be the Dunning-Kruger effect:
Thus, scientifically literate hierarchists may be more likely to let their biases influence their opinions on the causes of global warming because they have an inflated perception of their understanding the underlying science. This may also explain why we so frequently hear from engineers, geologists, and physicists who are skeptical of human-caused global warming despite lacking expertise in science. Because of their scientific backgrounds, they may have an inflated sense of their understanding about science, and thus draw incorrect conclusions that conform to their ideological biases.