I believe it is probably related to a desire to avoid exchanging cash, and whether any KLM customers want FF seats on Globalpass airlines in return. If KLM members are asking for FF seats on some TACA flights, they probably trade some availability. If KLM customers are not asking for Globalpass FF seats, then Globalpass would have to pay KLM cash for the seats (in whatever amount) and does not want to.

Just a guess as to why no KLM availability. (I am among those who have given up. Tried for a couple years to get KLM seats to Europe, and gave up.)

Djlawman