If by "so many" you mean some, the answer is because people generally buy into the culture's narratives when they lack the knowledge of what is really going on. Science explains these experiences extremely well. In short, lack of oxygen to the brain produces hallucinations that manifest in ways that reflect a culture's norms. These "Heaven and Hell" experiences are virtually unheard of in non-Abrahamic religion cultures. This is strong evidence to that the experience is no way objective, but like other hallucinations, subjective and imagined.
The claim that these images are formed when "the brain is dead" is simply false. There is no way to record when the thoughts are being formed, and people who have no brain activity for a period of time lose all sense of temporal order, meaning a thought they had before they died would seem like they just had it.
Again, people with generally no religious beliefs (technically atheists, but certainly not skeptics) will adopt a narrative of their culture (e.g., Heaven) and like all vivid dreams and especially hallucinations, they feel real. Lacking the scientific knowledge of what is going on, they default to adopting the belief of the culture, which they can accept cognitively, but solidified by a strong affective component (feeling) that makes them often hostile to any scientific explanation.
Bo Bennett, PhD
Social Scientist, Business Consultant
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