Vietnamese know if there is second Johnson South reef war again today, they will Lost all of their posts in Spratly islands, and USA will not come to help them.
USA trying to avoid war with their near peer counterpart, for this case China. because is something bad happen between them (China and USA), US Officials know the effect will be Catasthropic for their homeland, that's why they will avoid war with near peer counterpart, like China and Russia.
That's why vietnamese trying to cozying up with China now, and for China itself they trying to buying time.
If the status quo in SCS can hold up for another 5 to 10 years, it will be a Huge advantages for China.
Imagine this, China's Navy in 2027 is not China's Navy in 2017, in that time China already have 5 or 6 Aircraft Carrier, maybe more under construction and also hundreds of Modern Cruiser, Destroyer, and Heavy Frigate, Chinese Military big reform is also Done.
Muricans is not Stupid, they know fighting China is Suicidal for them, they definetly don't want hundreds of thousand of their kids, father, and husbands Die in vain only to help little viet to fullfil their territory ambitions