Seriously, who cares about the gains to other countries from TPP? This is just another example of poorly developed critical thinking skills on the part of many economists, the same silliness that ignores that most gains from migration accrue to the migrant as opposed to the host country.
If the mark of “good policy” or an attempt to sell “good policy” is to focus on people in other countries then clearly there’s something less wonderful than sunshine happening to the natives.
Think of this as a repeated game – if you know that the inhabitants of Country A always consider the welfare of Country B when playing their hand, then you’re going to exploit that in negotiations so most of the gains from the deal accrue to your country.
The idea that “poor countries” are charity cases that need free lunches from trade deals is silly. Re-read the literature on institutions – and think about how most of the gains from trade have accrued to the Community Party connected elite in China – and then keep asking “why?” until you bump into the inevitable conclusion that all of these gains from trade simply won’t “trickle down” to the poorer citizens except incrementally over long stretches of time.
The more likely outcome from TPP for the countries being discussed is non-trivial increases in luxury good consumption and capital flight, which, if you really care about the poorest people in these poorer countries, you would not support the watering down of the shallow capital or retained equity held by those firms experiencing the gains from trade.