I'll preface this by saying I don't really know anything about the Chinese Nuclear Energy Industry so I can't really give an informed opinion on the matter, but if I had to guess what makes Chinese nuclear reactors cheaper and faster to build, my guess would be that Chinese Government regulations surrounding nuclear reactor construction are looser than those in the West (and it makes sense on some level, China is a fast-growing nation and Party officials are probably more concerned about getting power plants built to meet rising demand than they are about potential disasters that may result), meaning that Nuclear Reactor designs in China can be simpler, lacking many of the same safety devices and controls that are mandated on Western nuclear reactors, and as a result are cheaper and faster to build, just like how Soviet nuclear reactors were cheaper and simpler than their Western counterparts as a result of lacking many of the features designed to make reactor operation safer and reduce the risk of a catastrophic failure.

The problem is it only takes one Chernobyl-scale catastrophe (and sometimes not even that) to bring the entire industry to a screeching halt and permanently damage the public's trust in the industry and confidence that it is indeed a safe source of energy to be pursued further.