As a news writer, I will guess that "The $25,000 Pyramid" is a) easier to write than "10-20-25-50-and 100,000 Pyramids", b) easier to read* than "10-20-25......" therefore easier for the viewers/listeners to comprehend, and c) the most-recognizable version of the show, considering it's the one most often rerun, even to this day.
Sometimes, going with the most common option is easier, especially when his career consisted of so many shows. If I were at the station tonight, I'd likely go with "The $25,000 Pyramid" or "Pyramid game shows" to keep it simple. The viewers are prolly aware of other versions, but don't need to know of the exact figures...
*Best way to annoy your anchors is make the copy difficult or confusing to read.