YANBU to think that no adult child would pay the sums on here.
Maybe that's the point: it's pitched so high for the parents who want their DCs to move out, but have no end in sight of that happening.
I only have one adult DC currently, but I do feel a bit sorry for friends and acquaintances I know, whose DCs are well in to their late twenties and early 30s, and still have DC at home. I expect that will be in years to come, when I'll have wanted them all to have left by then
.