well, because it didn't make much sense. why would albus be so scared when he's grown up his whole life in a wizarding family? (in harry's case it was justified because he was completely new to the whole thing and having spent his whole life getting the worst things couldn't dare hope to be sorted in the best house) jkr just put in that part to highlight the similarities between father nd son.
and how come ginny let harry name all their kids? she should've named one of her sons james.
the humour was forced in the ending, and after the action packed ending to the book, a scene showing 'a typical day in the lives of an ordinary loving wizarding family' would only work as an anticlimax. it was for this reason that jrr tolkein didn't write an epilogue (depicting a scene whee sam gamgee sits with his favourite daughter rose and tells her what happened to all his old elven, dwarvish and human friends) even though he had thought a lot about it. instead, he just told us i the appendix a bit about everything.
harry's profession wasn't indicated. we can only assume that he fulfilled his ambition and became an auror. nothing about spew, or ron's future.
and how can harry smile and think 'all was well' when most of the readers still hadn't got over the shock of remus's, tonks's and fred's deaths and the tragic revelations of snape and his consequent death?
then again, jkr ahd said she would be writing about what happens to the characters after they leave school. here a lot of well loved characters like luna, george, lee jordan, dean, seamus, etc were left.
but certain parts were good, nevertheles, and funny as well. but it's just taht i expected a bit more from rowling to end her famous series.