Note that the magus whose legacy is used to create the covenant, Leonardus of Jerbiton, was a member of Triamore until 1196 when he disappeared into Twilight.
Clusius also lived in Triamore for a few years. He arrived in the Spring of 1201 and left to establish the covenant in Fall 1204. You can take a look at what he was doing while in Triamore (and see a few seasons when he was elsewhere) in his Personal Journals.
That would be a good opportunity to establish a link to the covenant, which would explain the attraction of joining it.