What Edd said.
I think most people in Europe grew up with trilogos. So they have a great audience. It's a standardized card for almost the whole line having both English, french and spanish logo. Over the years the knowledge and variation of these have been researched and documented by many key collectors. articles, forums, books, etc have been written about it. The more the information is out there, there more collectable. Similar things happen with pre prod after Sansweet, Guz and others researched, wrote and published. Proof cards were basically given away. 1,2,3 or 4 books later they are the hottest thing around.
It's still an exiting thing to collect, as not all is known about trilogos. More is to be discovered.