Why does you CGPA even matter

Prospective pre med here (rising senior in hs)

Ik at this point that there's a Cgpa and an Sgpa (for the main pre reqs)

Coming to the question, if I am an engineering major with an ass cgpa but I do well in the pre reqs and get a good sgpa, why is that bad? What determines if I will be a good physician is how well I understand the life sciences, chemistry, etc., so why does an engineering gpa even matter to them?

I've heard someone on this sub say "Med schools prefer someone with a 4.0 in underwater basket weaving than someone with a 3.3 in fundamental physics."

Is this even true?? If yes then it's downright absurd. Med schools need to see the difference in difficulty between engineering and some super inflated humanities major