Vitamin D is preventative in nature. Also there are trials here...look them up on clincialtrials.gov
https://clinicaltrials.gov/study/NCT05633472
https://clinicaltrials.gov/study/NCT05356936
https://clinicaltrials.gov/study/NCT05633472
https://clinicaltrials.gov/study/NCT05356936
How do you mean "preventative in nature"? Are you aware of any studies which a/b tested Vitamin D on active respiratory tract infections which showed that the Vitamin D has no effect in this situation?
I’m just calling out the fact that your complaint is not rooted in reality.
The studies you refer to are observational tracking people who supplement vitamin D or live in places where they get it naturally more. To say vitamin D is the cure to most things or even long covid is shortsighted and frankly irresponsible. Linus Pauling did that with vitamin C and tainted public opinion on vitamins.