in 1973 there was the "coup" of Pinochet and I suppose this lead to a certain "isolation"; everyone tried to avoid playing Chile.....
Yes, but "Golpe" was in September, while those friendlies were in March. I don't have a sure answer, but I think the reason was the fact that, in
the very same period, Colo-Colo had to face several engagements in the Copa Libertadores
so, as the National team was mainly composed by players from such club,
they probably preferred to cancel those friendlies, giving the priority
to the Copa Libertadores.