Because he was a headliner in a third world country that can't into archiving videos. Even now they have to steal clips from cubsfan. In fairness, most US and Canadian wrestling from before the 80s is lost too because stations just threw the films away. The only two countries that have wrestling from that time period archived are France and the UK, and the British stuff is locked away in a TV archive. Japan has some too, but not as much as you'd think. The only reason more Japan TV wrestling from the mid 70s onward is available is some high executive guy was a geek for both technology and wrestling and had a video recorder which was cutting edge technology at the time.
