South Korean here. To me, RCEP seemed like an obviously good thing to sign, and I am shocked that people in US are shocked or that they think SK should fear alienating US. TPP is irrelevant since SK was never a party to TPP.
I find it unfortunate, but I recognize that as a newly minted culture exporting nation South Korea at large is in favor of stronger copyright enforcement, and that my personal opinion that copyright is currently too strong and detrimental to culture holds little sway.