Probably because their best guy had to pull out because of an injury and they screwed up during qualifying rounds. Whoever did get the slots probably didn't have good enough scores to be in the finals.
I Dunno about that, while it was announced a couple of days ago that Koji Yamamuro was pulling out, and was being replaced by Tanaka there was no such mention of any changes in the Chinese team and it does seem unlikely that the Chinese would not contest the event at all.
All gymnasts compete in the qualifying rounds to get a ranking which then determines their eligibility to contest the events. It appears that no Chinese gymnast achieved a high enough score to be in the top 24. That has got to be a long term worry if none of their top 5 can beat a score posted by the usual "Cellar Dwellers" of the sport in such as Britain Belgium Italy Israel Spain. Actually Spain and Germany qualified 3 but the rules only allow 2.
Actually IMO and from what I've seen of the Chinese gym team, they have'nt been all that convincing for the last couple of years. In some of the events, they won not because they were good, but because the other team blew it. However I hope they can turn it around for the rest of the contest, but like the Russians did I think they need a team rebuild as the other countries are catching up fast in skill levels. IMO the old power houses in gymnastics cannot think that they will be assured of medals by just turning up.
The US woman who was world champion messed up during qualifying and she's not competing tomorrow either.[
Actually she did post a score high enough to qualify 4th I think but as the rules say, only two from each country. SEcond and third is not qualifying spot is pretty good for the US although the Russian might prove too good