The point is that the floor is the lowest. There is no basement in this. The facts do not allow the floor to be set lower then 21. We could theoretically set it lower, if we had different information, or good reason to believe the information we have is somehow misleading.
I agreed with Peelee's original description, however I thought he said it in a potentially confusing way, and we certainly seem to have one confusee amongst us. If we had different information the floor could maybe go up, but at this point in time it needs to be as low as it is.
If you've played a game with a confusing nomenclature that I haven't, bully for you, but that doesn't make that nomenclature correct, no offence intended.