If you put yourself in their shoes, you realise that you have to give advice for the 10-20th percentile parents (or worse) because you are giving the same advice to everyone.
The alternative would be to offer more complex advice such as "if X Y and Z then do A, if only X do B", but the perception is that's too difficult for people to follow.
So you end up making very defensive (and therefore onerous) recommendations.
An interesting fact is that, since the introduction of the "baby sleeps on their back, alone", SIDS has gone down, but flat heads have gone up. It's probably been a good tradeoff, but it's still a tradeoff.
Also, I've seen a second time mother refer to "don't cosleep" advice as "western nonsense" which I found funny because it puts things in perspective - vast swathes of the world think cosleeping with your child is safe, natural and normal.