Obviously a parent who is spending nearly all their time with a newborn knows them best and is likely able to make the best judgement about what works for the child, but the purpose of the advice is to avoid a class of scenario that occur most often. due to issues that are very difficult to detect and often go completely undiagnosed, as they pertain to early development and often improve naturally over time.
The technical report by AAP the other year does an excellent job of presenting the current evidence in an as objective way as possible, I highly recommend it:
https://publications.aap.org/pediatrics/article/150/1/e20220...
You will note that efforts are being made to disentangle diagnoses from the broad SIDS label and that while SIDS cases are trending downwards, it's likely due to both proper classification and education.
The point of preventative measures is to avoid the issue entirely. Sure, tummy sleeping might not be a problem for you (or maybe it was and you just got lucky!) but by generally recommending back sleeping, a class of issues is avoided.
So all in all, I really don't see this as bullshit at all. Caveat that you gotta do what you gotta do, but I'd rather this advice persist than not. We should hope that no one ever has to endure the loss of a child.