It's probably just due to the insanely tiny budget that NASA has. Their budget is great for probes, but not to support manned spaceflight. :/
The Chinese space budget is estimated at ~ $2 billion/year.
NASA's budget is $16.6 billion/year
Either NASA is wasting a shit load of money on bullshit or
the Chinese are a lot more efficient.
In either case - it's obvious they are doing more with less than we are.