While for US domestic itineraries a round trip ticket can be pieced out to two one-way tickets with exactly the same total price (IN GENERAL, as I know someone will come with the anecdotal example when this is not true),
this is not the same for international itineraries.

One way tickets into the US (or out of the US) will always price at a high fare bucket. This is true for all airlines, not only for LATAM.

As for the thread title, I find it to be an uncalled for generalization as there are plenty of examples where one can find extremely reasonably priced LATAM tickets. I am sure there are plenty of examples in the other side of the spectrum (expensive). In other words, LATAM is neither cheap or expensive, it just prices out according to the market. And I was being sarcastic about changing the thread title.