That's the trouble though Hula.
One or two books about pants or poo, okay, it's a bit funny and the kids laugh it them.
Then everybody jumps on the bandwagon for an easy bestseller about dinosaurs shitting green diarrhoea for several pages and you end up feeling less like you're in the children's section of a bookshop and more like you're visiting that particularly grotty public toilet from Trainspotting.
It's like you don't need a proper story anymore, as long as someone shows their bottom or does a poo on something before the end of the book.
DS (just 6yo and normally keen on this sort of thing, especially if he can laugh in a Minion voice and say "butt") reads a lot of books, we have those dinosaurs and aliens in underpants books (and I hate them) and but there's only so much toilet action a bookshelf can take.
They might have sold well because they have the word poo in them and were marketed well because he's famous, but they're not very good are they? There are better, funnier books out there, even in the 'pants and poo' genre itself.
The Mole Who Knew It Was None Of His Business, for example. That's a book about poo that is actually quite good and funny.
It just seems quite cynical and unoriginal now, as though they thought 'I fancy writing a book, and I know, kids love dinosaurs and poo, so job done. Just need to make it rhyme.'
There are loads of books of this type out there now, and very few of them are good.