The mainstream is not interested. Look at what happened to Pauling. He won a Nobel Prize for his work on vitamin C. There should have been much more research done after this
Just a small nitpick. Linus Pauling did not win a Nobel Prize for his work on Vitamin C.
His Nobel Prize in Chemistry was for his work describing the nature of chemical bonds.
There was more research into vitamin C after Pauling. That is how we know that megadoses can cause nausea, vomiting, diarrhea, flushing of the face, headache, fatigue, disturbed sleep and rashes.