Why why why?

Why complete a mystic cycle, which titillated the imagination of many readers and moviegoers, this way ??
The novel revolves around Dave Bowman, back on land, adapting to life in the early 4th millennium ...
If the description of the life of the earth's population, packed into giant towers, whose higher floors are virtually in space is quite interesting (think elevators leading outside !! :-)
The story in itself, quite flat, ends in a rather brutal and rather disappointed me.
In the end, some revelations about the role and functioning of the monoliths can justify buying the book for those who want to know and are ready to lose their illusions ...