Why does China finance US fiscal deficits and bailouts

I read the news (here) on China is financing US stimulus package by financing the US treasury bonds. Currently, China is the biggest creditor to US in term of USD 1 trillion.

But here come the plead by the China premier to US ,"Do not devalue your currency through reckless spending". The reason given by the China premier is that he wanted his asset (credit given to US) to be safeguarded. Simply, it means that if US dollar devalues, then the USD repatriated back to China is devalued to the stage that does not gives any return.

This is a paradox. It seems that the China premier is doubtful about US investment return which may bust when and if US goes bankrupt.  But China is willing to become a lender.This shows that China as the previous banker of US have no way other than to continue financing USA in order not to let it goes bankrupt. IWhy ? If, US goes bankrupt, then all the money currently tied in the US treasury and bond will melt together with the USA banking system. It looks like China is really-really tied up with USA, no matter which direction US goes, China has to bow.

There is another problem. Previously, China and other countries are willing to finance US because US is the buyer of their goods. By buying US treasury, yuan or remimbi are converted to USD. When this is done, the value of USD will appreciate. Once the value of USD appreciates, China made goods becomes more competitive than US made goods and hence will be bought by US consumer. This type of arrangement provides a big market for China and Asian countries. 

However, in the wake of the biggest economic crisis of the world, how much more  these type of arrangement can be done in the future ? US's consumer is very laggard nowadays. They have losses their home and now can't even own a car.

More so, one of the reason of the existance of US economic problem is it's very big trade deficit with China and one of the way which US can overcome this problem is through devaluing it's currency so that the trade deficit is narrowed. This is the most orthodox but effective way when we look at trade balances.

My thoughts about this matter is that the best way to help US to regain it's feet back ( and help China to sell your goods in the longer term) is to let Yuan appreciate in the short term ( a few years). Once the bond has reach it's maturity, it is better for China to purchase other types of assets (physical or stocks) in USA. Only when US economy has become stronger, then Yuan can slowly depreciate compared to USD and hence a more healthy trade quantum can be achieved in the future.

If China insists to keep on financing and also keep on ensuring that US trade deficit is balooning, sooner or later this bubble will bust and this will be very-very bad for the whole world.