The potential motives of Ventura aside, what was more important was the news that Ventura had a monopoly on the Primordial Garden. Lex had learned long ago that anything with the word Primordial in its name was hella special.
If this was a video game, the Primordial descriptor would be equivalent to a grade, or even several grades above legendary - whether the ranking be for items, places, beings or anything else.
If Ventura had a monopoly on the Primordial Garden, was that really something he wanted to mess with? Even if he had the guest in front of him as a deterrent, Lex had not forgotten that when he completed the quest related to Pvarti's wedding, one of the things that upgraded his reward was the presence of a projection above the Dao realm.[1]
With no other information at hand, Lex could only assume that the projection of the being above the Dao realm was associated with Ventura.
