It kind of makes sense for Treta Yuga to be the default Yuga, as its number of legs is the average number of legs:
(4(4)+2(2)+1(1))/(4+2+1) = 3
i.e., If you average the dharma in all Yugas you get the dharma in Treta Yuga as the default yuga.
Still, I don't know where this author is getting the realms of perpetual Treta Yuga from, so I would like a scriptural source for this idea. So does any scripture enjoin Treta Yuga as the default state of Dharma ?