Because they sell supplies to many other people than the ones who purchased spas from them?
I don't know.
But I have sold Baqua for quite a while now, and we try to let folks know that it eats Polycarbonate - such as some light lenses and some jet parts.
We try to determine if the spa the Baqua is destined for is new enough to have the updated lens or not. But we don't catch them all.