Why Shouldn’t Babies Sleep In A Boppy Lounger?

This may be a dumb question, I’m sorry. I’m aware that there is a warning on the lounger stating that baby’s shouldn’t sleep on it. I’m just curious how it would harm them? I tried looking it up and it just says that adult supervision is needed at all times when baby is on the lounger. Please educate me more , thankyou ❤️