Who said anything about isolationism?  Its about leveraging one's power/advantage to gain more.  America first!

"Future after US withdrawal
TPP's future was uncertain given US withdrawal, but several signatories signaled their intentions to rework TPP without US participation. For instance, Australia's Trade Minister Steven Ciobo responded to the US withdrawal by stating that he had spoken to other leaders of TPP member nations to discuss 'ways to lock in the benefits from the TPP' without the US as a party to the agreement. New Zealand has proposed an alternative deal without US participation. Shinzo Abe has, however, stated that TPP without the US would be 'meaningless'."

"Nobel Memorial Prize-winning economist Paul Krugman has said that 'there isn't a compelling case for this deal (TTP), from either a global or a national point of view.'
https://en.wikipedia.org/wiki/Trans-Pacific_Partnership