Interesting that the answer to the question seems to be related to hybridizing.
I thought more people considered parentage when buying daylilies.... Even when they don't hybridize.
Maybe Rice's are on to something. If collectors don't care, and hybridizers, in general, will buy the plant even if parentage is not listed...why bother with all the bookkeeping?
And, even if they keep track of parentage for themselves, by not listing them when registering, others cannot make the same cross instead of buying your intro. (and, I realize that you could make 10,000 seed and not come up with the same plant, exactly, that the hybridizer did.)