Those countries do have agency, they do participate in discussions and sign treaties, they just keep increasing CO2 emissions.
Per capita does not matter, totals do. Would it make a difference if Switzerland stopped emitting CO2 completely and no one else changes anything.
You cannot change the past, you can change the future. Unless those countries follow the same standards as the west (and very, very soon) then CO2 emissions are going to keep rising. Right now China has single companies that emit more CO2 that the whole of the UK, they are building coal powered power stations, and generally not giving a fuck. They see advantages in arctic ice melting and temperatures rising, as does Russia.
It is reasonable to say they cannot be expected to follow higher standards because they west did not, BUT only if you are willing to accept that CO2 emissions will therefore keep rising.