Upon the ill advised retreat of the US from SEA, SEATO fell apart. The core of SEATO was Thailand. In the late 1970s, under guidance from the USSR, Vietnamese troops took over Cambodia and eventually made incursions into Thailand. Lacking the once present US troops and bases, Thailand went to the PRC for help. A few months later, the PRC made an incursion into Vietnam. Thailand has, ever since, taken a path of relative neutrality vis a vis the US and the PRC. Meanwhile, the other remaining SEATO countries that did not fall to Communism during the 1970s have taken the Arabist / Islamist tack. While there has been a slight thaw more recently, none of them are reliable.
Do you have a source for this?