The plot, while centered on Trout, is also a sort of ramble in which Vonnegut relays tangents to the plot and comes back dozens of pages later: the timequake has thrust citizens of the year 2001 back in time to 1991 to repeat every action they undertook during that time.
It can be speculated and reasonably defended that in his advanced age Vonnegut no longer felt up to the task of composing a conventional novel in the same way he did before.