Because the last thing the US & the west wants to do is drive Vietnam into China's hands.
Secondly, given the standard in the entire world, it's probably an above average country at this point on human rights and getting but slowly but surely better, esp given it's rapid industrialization comparable to South Korea & Taiwan in the 1980s atm (that use to have not a great record on those issues either).
If you complain about stuff like gay marriage not being a thing, it's only legal in Taiwan as of know, and about to become so in Thailand.
If we'd sanction the entire world for this, good luck sanctioning 150 countries, especially since some Florida legislators also want to sanction Spain, Norway & Ireland.
The only one you'll end up sanctioning is yourself if you sanction the entire world.
